Emil Heitz (1892- 1965): Chloroplasts, Heterochromatin, and Polytene Chromosomes

Anecdotal, Historical And Critical Commentaries on Genetics Edited by James F. Crow and William F. Dove

Helmut Zacharias Windmuhlenberg 6, 0-24631 Langwedel, Germany

ANGLED nuclear threads:EMIL HEITZ is frequently personal communication) and at Wurzburg University T said to have discovered, together with HANS (HAUPT 1932;J. GREHN,personal communication). BAUER,polytene chromosomes in Diptera. What is in- The longitudinal differentiation of mitotic chromo- correct in this statement is the word “discovered.” Pri- somes became apparent, and the terms euchromatin ority for this should go to BALBIANI(1881). But at that and heterochromatin were coined (HEITZ 192813). time the phenomenonwas understood as a tangled con- Chromatin is the substance that transforms into chro- tinuous thread, called spireme (TANZER 1922;KAUFMANN mosomes during mitosis ( BOVEIU 1904). According to 1931). An early suspicion that the oversized structure this view, euchromatin is chromatin proper, the chro- might consist of individual chromosomes was coupled mosomes that are structurally altered during telophase to the idea of a constant number of elements (RA” so that their individuality is not recognized in the nu- BOUSEK 1912; for review, BEERMANN1962). This postu- cleus. Heterochromatin behaves differently from eu- late could not be tested as long as tissues containing chromatin in morphogenesis; specific (parts of) giant nuclei were cut intomicroslices. The difficulty was chromosomes do not participate in telophase reorgani- overcome when the technique of tissue squashing was zation (HEITZ 1935). applied by a botanist at Hamburg University. Hetero- Heterochromatin in Bryophyta: Using the liverwort chromatin could now be studied as a general property Pellia epiphylla Uungmaniidae) and exploiting pro- of chromosomes. phases, metaphases and telophases as well as interphase It is fitting to discuss the history ofideas about hetero- nuclei, HEITZfound evidence that identical chromo- chromatin at the presenttime. There has been a recent some sections are constantly heterochromatic (hetero- resurgence of interest in heterochromatin, as molecular pycnotic). Heterochromatin was found without excep methods provide a way to study the subject at a deeper tion in all genera of acrogynic liverworts(HEITZ 1928b, level. This is also evidenced by several recent articles in p. 796), whereas in anacrogynic species the heterochro- GENETICS,including one by LE et al. in this issue. matin of autosomes depends on thepresence of a heter- TheHeitz method Avoiding the time-consuming opycnotic minute chromosome (p. 801). “With 70 spe- use of a microtome, HEITZ(l926,1928a,b, 1933a) fixed ciesof true mosses from 20 families, always one plant material in two parts of alcohol and one part of chromosome behaves differently. It does notdisappear acetic acid. He then stained it in carmine acetic acid in telophases as do the other chromosomes” (p. 815). (45%) and prepared, with needles, a single cell layer. HEITZprovided evidence that heteropycnosis is not an STEVENS(1908) and BELLING(1926) hadintroduced artifact. “Initially, it was expected that it must also be similar methods. However, to obtain the best metaphase observed in vivo, at least in resting nuclei (in in- spreads free of cytoplasm, HEITZ applied gentle pres- terphase). Nuclei of fully grown cells lyingat the outer sure to the cover slip. Thus, the specimen was attached cell wall and not greatly obscured by chloroplasts show to the slide and was prevented from being carried off the heterochromatin very well” (p. 790). “The cause when the slide was thoroughly boiled. Later, the more of heteropycnosis can only lie in the concerned chro- delicate Dipteran tissues were not boiled but cautiously mosomes themselves” (p. 815). heated. “Thedescribed preparation can be done within “It may arouse amazement that the outlined facts a moment after some practice. Within half an hour, 4- were up to now overlooked. However, without the boil- 6 specimens can be produced” (HEITZ 1933b, p. 726; ing method I would not have visualized the regularity 1936). This technique, nicknamed hei(t)zen (heating), of the phenomenon so soon. The advantage of my was adopted first at the Kaiser-Wilhelm Institute in Ber- method, apartfrom saving time, is that only chromatin lin-Dahlem (STERN1931; GEITLER 1962;G. MELCHERS, becomes intensely stained, whereas plasma and above

Genetics 141: 7-14 (September, 1995) 8 H. Zacharias all the nucleoli scarcely take color. Thus, one need not arrangedaccording to MORGAN’Sconclusions from search for the right degreeof differentiation, since any transmission genetics. Now, for the first time, the new properly prepared specimen is, by itself, correctly dqfer- technique demonstrated a longitudinal differentiation entiated” (p. 802). Boiling in aceto-carmine had pro- in cytological entities, euchromatin and heterochroma- duced the first C-banding patterns ( PASSARGE1979). tin. Heteropycnosis characterized not only sexchromo- Heterochromatin “inplants and in substantial details somes (SHOWALTER1928) but likewise autosomes. Fur- also in animals was hitherto an unknown phenome- thermore,heterochromatin was aphenomenon of non” (HEITZ 1928b). Therefore, he started aseries of general biology occurring in both animals and plants. cytological investigations searching for heteropycnosis Therefore, Professor WINKER (who had coined the in somatic cell nuclei of Diptera. term genomein 1920) “generously put at my disposal the Heterochromatin in Drosophila: The Physical Basis of resources of the Botanical Institute for these studies.” Heredity by THOMASHUNT MORGAN (1919) became well HEITZ(1929, 1932) had imagined that “euchromatin known in Germany through an authorized translation is genicly active, heterochromatin genicly passive. Het- by HANS NACHTSHEIM(MORGAN 1921). The book and erochromatic chromosomes or pieces of chromosomes contact with the “genetics community” (HARWOOD contain no genes or somehow passive genes.” However, 1993) stimulated EMILHEITZ (1933b) to breed at least the results from MORGAN’Slaboratory (MORGANet al. five Drosophila species in the greenhouse. Drosophila 1925; MULLERand STONE1930; MULLERand PAINTER funebris was caught in the Botanical Institute Hamburg. 1932) forced a revision: “My ideas are not correct, be- The species waseasily recognized, from the chromo- cause genes which lie within the heterochromatin do somes. D. melanogaster was received from CURTSTERN, intervene in the developmental process of an organism. Kaiser Wilhelm Institute for Biology in Berlin-Dahlem. Nevertheless, the density of genes in a chromosome is D. simulanswas from the Institute for Experimental Biol- related to the longitudinal differentiation in euchroma- ogyin Moscow, mailed by Fraulein Dr. FROLOWA tin and heterochromatin. Euchromatic pieces are rich, (1925). D. hydei and D. virilis, “originally from the whereas heterochromatic ones are at least poor in genes. United States,” were from RUDOLFGEIGY, Zoological One has to suppose further that the genes are evenly Institution at Basel. and linearly distributed within the euchromatin” (HEITZ The first attempt was made with the MORGAN fly. 1934a, p. 266). Interestingly, he discussed whether the HEITZ (1930) was surprised that cells from different Drosophila genes light and rolled are within the euchro- organs of larvae and adults gave pictures similar to those matic or heterochromatic environment (p. 264). known in true mosses. He saw one and sometimes two Polytene chromosomes: HEITZwas promoted from vacuolated and intensely stained blobs of chromatin Privatdozent to extraordinary professor in July, 1932. At during interphase. that time, BAUERworked as a postdoctoral fellow and Since D. melanogaster appeared “rather unfavorable scientific volunteer in the Institute for Marine and with respect to cytology,” HEITZ (193313) continued Tropical Diseases at Hamburg. There he became ac- with D. funebris. Its karyotypewas known to contain two quainted with the Feulgen procedure as being specific remarkably large chromosomes of similar length in for the chromosomal substance (BAUER1932). HEITZ both sexes (METZ 1916, 1926). However, while one of (1931) also was aware of this, but he preferred boiling these chromosomes (the Y) was totally heteropycnotic, in carmine acetic acid because he could not discrimi- the other was differentiated into a euchromatic half nate heterochromatin and euchromatin with the Feul- and aproximal heterochromatic section. With the find- gen technique (HEITZ 1935, p. 409). A joint venture ing of partial heteropycnosis in the X, a new “structural had beenstarted with a very convenient subject contrib- type” of sex chromosome was detected. This was in uted by HEWN WEBER(1933), a recognized ento- contrast to the known “quantitative type” where Xand mologist at Danzig. The results from the black “hairy Yare of different sizes. garden midge” were considered so important that the After these preliminary examinations, HEITZ(1934a) manuscript was submitted on July 31, 1932.Thus, “Evi- returned to D. melanogaster and added D. virilis. The dence for the chromosomal nature of nuclear loops in sex chromosomes of these species likewise were of the the tangled nuclei of Bibio hurtulunus L.” (HEITZ and structural type just described for D. funebris. Further- BAUER1933) appeared ahead of the Drosophila papers. more, partial heteropycnosis characterized the au- The authors had followed their standard procedure tosomes. The fact that heterochromatin is proximally of chromosome analysis: first of all, one has to investi- localized in any autosome was termed “equilocal heter- gate mitotic prophases and metaphases, after which PO- ochromacy.” Figure 1 summarizes the findings on het- lytene structures can be analyzed. Somatic mitoses were erochromatin distribution in somatic nuclei of the obtained from neuroblasts and follicular epithelium of three Drosophila species. ovaries. Prophases in B. hortulunus showed five pairs of Introductory remarks (HEITZ193313) described the chromosomes that separated into 10 metacentric ele- main research impetus. (i) Chromosomes are the mate- ments in metaphase (p. 69). rial substratum of genes. (ii) The genes are linearly Tangled nuclei were found in salivaryglands, midgut, Perspectives 9

FIGURE1.-Schematic summary of chromatin structures from three Drosophila species. Longitudinal differentiation in euchromatin and proximal heterochromatin is evident in metaphase configuration. The heteropycnotic material is associated with one or two chro- mocenters in interphase nuclei (HEITZ1934a. Figure 9; 1935, Figure 7).

Malpighi tubes, and occasionally in the brain. Especially work) on a ‘new method’ for thequalitative analysis of from the Malpighi tubes it became clear that the large Drosophila melanogaster chromosomes. Painter’s state- nuclei did not containa continuous thread.There were ment ‘It has long been known . . .’ was not correct at always five clearly separated thread sections, each dou- all. Evidence for the chromosomal nature of nuclear ble and different in length. Furthermore, structuralfea- loops was demonstrated initially by our work. Clear ob- tures (nucleolus and terminal peculiarities) were not jections must be raised to the mode of Painter’s ac- randomly distributed butwere found characterizing the count” (HEITZ 1934b, p. 588; see also PAINTER1933a, individual nuclear loops. Last but not least, they were 1934b,c, 1935). Feulgen-positive. The results led to the conclusion that It is noteworthy that the “greaterdetails” had already the giant threadsare twin chromosomes in haploid been submitted to GENETICSin May, 1933, but unfortu- number (p. 72). Thesynapsis of homologous chromo- nately appeared one year later (PAINTER1934a). somes was later employed extensively as a simple way The objections obviously were taken into account, to detect heterozygous chromosomerearrangements and therephrased sentence reads, “All cytologists have (PAINTERand STONE1935). known for a long time that in the salivary glands and Contest for priority: “The most striking recent devel- other tissues of the larvae of Diptera in general there opment in cytology is the discovery of the chromosomal occurs what has been called a ‘permanent spireme.’ In nature of the long known giant structures in the nuclei the nuclei of such tissues structures called chromo- of the salivary glands of Diptera. This discovery, made somes are very large and show very conspicuous bands” withBibio (Heitz and Bauer 1933), was extended to (PAINTER1934~). Troubles came not only from PAINTER Drosophila by Painter in 1934” (STURTEVANTAND BEA- but also from the young co-author. HEITZ(1933b, p. DLE 1939, p.364). In Hamburg, both authorswere aware 723) complained in a footnote, “Bauer (1933) has just of their achievement. “Heitz and Bauer (1933) have pro- reported on partial heteropycnosis in the oocyte nuclei vided the final evidence with Bibw hortulanus and thus for of Dytiscus marginatus. My assessments on partial hetero- Diptera generally that there exist enormously enlarged pycnosis in Drosophila funebrk, D. melanogaster and Sca- chromosomes” (HEITZ1933b, p. 727). tophila unicornis were made earlier than those of Bauer No earlier than December, Science published a pro- with Dytiscus which is not quite obvious from his ac- vocative statement by THEOPHILUSSHICKEL PAINTER count.” (1933b) on polytene chromosomes in D. melanogaster A burst of research in the new field of cytogenetics “It has long beenknown that in the functioningsalivary hadbeen initiated ( HEITZ 1935, p. 429). LOTHAR glands of many dipteran larvae the chromosomesshow GEITLER(1934) reported on polytene chromosomes in an elongated and annulated structure.”HEITZ immedi- Simulium, KING and BEAMS(1933, 1934) dealt with ately and harshly commented, “Almost one year after Chironomus, and METZ and GAY(1934a,b) with Sciara. the publication of our investigations with Bibio hortula- WUSPATAU (1935) focussed on D.simulans, and C. C. nus and shortly after the appearance of the said work TAN (1935) did so on D. pseudoobscura. THEODOSIUS (on D. melanogaster), Painter reports preliminarily (not DOBZHANSKY(1935) recognized that D. miranda was dif- less than three times, December 1933,1933,1934) and ferent from the sibling species D. pseudoobscura, as in greater detail (1934, here giving reference to our shown by the banding in polytene elements. 10 H. Zacharias

Natural banding pattern: The constant structural able to do this . . . Theheterochromatin proper is characters of polytene chromosomes were already ap- named a-heterochromatin from now on. The adjacent parent in the first approaches. Especially the discontin- heterochromatin, like the former, does not reveal any uously banded pattern of the giant nuclear loops was differentiation in chromomeres, but has the capability recognized, proving the individuality of the chromo- of growing in common with the euchromatin. This p- some pairs. “The loci of these chromomere-like disks heterochromatin, as it might be called from now on, are not randomly distributed but constant. This consti- possesses only a minor extension and cannot be recog- tutes new evidence that chromosomes possess a con- nized as such in somatic prophases, while the a-hetero- stant differentiation in the direction of their longitudi- chromatin makes up half of the rod-shaped chromo- nal axis” (HEITZand BAUER 1933,pp. 78, 81). somes’’ (HEITZ1934b, p. 596). The constancy of polytene bands was also detailed in Contemporaneous researchers had explained that a following paper (HEITZ 1934b), and thetransatlantic chromosomal growth is caused by chromatid multiplica- success was acknowledged: “The usefulnessof giant tion. Thus, theoriginal definition of a-type heterochro- chromosomes of Diptera for localizing exactly the matin corresponded to suspension from endoreplica- (Mendelian) factors was shown for the first time by tion rather than to condensation. However, PAINTER Painter (1933, 1934), who had collected rich material (1933b, p. 586) had discussed alternative mechanisms: for investigation” (HEITZ1935, p. 433). Further, “One “Either the inertmaterial of both theX and Y has been has to emphasize the work of Bridges (1935), who has eliminated during ontogeny (of D. melanogaster),by carried forward the analysis of longitudinal differentia- diminution or some similar process, or this material tion in this species (D. nzelunoguster) so far that it is exists in the salivary nuclei in some unrecognized form difficult to beat. Furthermore, Bridges has established not visibly connected with the chromosomes.” The idea a very useful system of assignment” (p. 430). of elimination probably goes back to Wurzburg where Multistranded elements: The size of the novel chro- PAINTERhad spent several months in1913-14 with mosomes was initially described as “magnified” and THEODORBOVERI (WAGNER1970; BOVEIU 1910). But “giant” while the term “polytenic” was introduced by HEITZ(1935, p. 433) remained persistent: “The hetero- KOLTZOFF (1934). GUNTHERHERTWIG (1935) noted chromatin of the Drosophila species is also present at thatthe gigantic dimensions are achieved by real the giant chromosomes. Painter, who believed earlier growth, i.e., by multiple doubling of thegenome: (1934) that the inert region would be eliminated in “Thus, any gene is present in the salivary gland chromo- the loopcontaining nuclei, as he could not find an somes of D. melanogaster at least 256-fold or 512-fold, equivalent, has recently (1935) joined my opinion.” and not only 8 times as Koltzoff (1934) and Bridges The HEITZhypothesis of under-replication in larger (1935) recently thought. . . . A substantial point in the somatic nuclei was also attacked by BAUER (1936, p. discovery of Heitz is that not the number, but only the 217), then a research fellow at the California Institute sizeof the chromosomes is increased in the salivary of Technology in Pasadena: “Observations in Chiro- gland nuclei. These giant chromosomes lie in enor- nomidaeled me tothe conclusion thatheterochro- mously enlarged nuclei.” matic regions of salivary gland chromosomes are com- Also HEITZ (1935, p. 430) refers to these papers: posed of the same number of chromonemata as the “Bridges (1935) and Koltzoff (1934) independently euchromatic strands, the difference between them be- have explained the giant sizeof these chromosomes ing due to the structure of the single chromomeres.” this way: There is not a single and strongly enlarged Regarding D. pseudoobscura, Figure 5 in his paper is a chromonema. The thickness is brought aboutwhen the diagram presenting thetwo types of chromomeres with- multiplied chromonemata remain in mutual connec- out local under-representation of chromatids. tion between each other.” (Nowadays we preferthe HEITZ dismissed:Looking back, shortly after his sev- word chromatid instead of chromonema.) entieth birthday, HEITZwrote to CURTKOSSWIG, then An explanation of the extraordinary size must con- Dean of the Faculty of Mathematics and Sciences, “It nect the giant structure with the “normal” chromo- is for me speciala honor to be made an honorary doctor some. In this view, BAUER(1937, p. 72) hassummarized, by the Faculty of the University of Hamburg because I “Thus, the giant chromosome is a bundle of identically actually havemade my most essential works at the Insti- built fibrils of which the homologous parts are at the tute for General Botany there.” He had joined the staff same level.” in November, 1926. Heterochromatin under-representedBecause D.vir- However, on February 4, 1937, EDGARIRMSCHER, the ilis possesses some 50% mitotic heterochromatin, it was curator at the Institute for General Botany and thus a assessed as especiallysuitable for investigating chromo- close colleague of HEITZ,wrote an official letter to the some development in the soma. “While euchromatic Rector of the Hamburg University. IRMSCHERdid so as sections of the chromosomes increase to gigantic size the Gaudozentmfuhrerof the National Socialistic German during the growth of the nuclei, the heterochromatic Labor Party. He reported to the Rector, Prof. ADOLF sections, united in a collective chromocenter, are not REIN, “that Prof. Heitz who, under the law, has to be Perspectives 11 regarded as non-Aryan, will give a lectureUNMZRSlTY on heredity.” GOVeRNMENT The Nazi official recommended cancellation of this lecture, otherwise certain circles might make trouble for the University (ROLANDHEITZ, personal communication; Hamburg Staatsarchiv 1937). The Rector immedi- ately conferred with HANS WINKLER,director of that institute. Because of this intervention, HEITZchanged his lecture title to “General Genetics” for the rector’s files, although the formertitle “Introduction to Hered- RECTOR I ity” had already been printed in the lecture timetable (Hansische Universitiit 1936). Hamburg JUudon Authority Jun 29, e:Any Jewish Faculty for Medicine More serious consequences arose from the notice must be dsrmsscd wthout delay. that HEITZwas not pure Aryan. His maternal grandfa- Jul7, Cmfidential leacr: Prokmor Heik is 25% Jewish. ther, Dr. MORITZSCHWALB (1833-1916), had beenJew- Hamburg Education Authority I ish and a protestant clergyman. From 1867 to 1894, he served as an elected parish priest in Bremen and became known for his critical and liberal sermons (SCHWALB1884; HUNTEMANN1969). IMPERIAL AND PRUSSIAN MINISTER The German Public Servant Law hadjust been FOR SCIENCE, TEACHING AND NATIONAL EDUCATION, klm amended on January 26, 1937. According to $25, an Aun 17. orda: Heik is aLcn off b ProfesurEmilHeik official as well as the spouse had to be of German or related blood. Thus, even partially Jewish descendants Aug 15: Defem lelter. Hamburg Stateoffice ’ were not allowed to teach at German universities Aug 27, orda forwerded. (BRAND 1937).A cascade of documents, produced by 1 I the university and the government, culminated in a Hamburg Educatjon Authority A Aug30, ordafommkd. claim for the dismissal of HEITZas nonpermanent ex- - I RECTOR Sep 21: Short answer. traordinary professor (Figure 2). However, the aca- Oa 1, Rector’s Communiation, no. 25: demic grade Doctw habilitatus expressly remained un- “Rofessor Heih has left the taching staff.” touched. FIGURE 2.-Dismissal of HEITZfrom Hamburg University A letter written by HEITZpointed out that he was 3/4 during 1937 (Hamburg Staatsarchiv, Hochschulwesen 1937). Aryan.His paternalgrandfather, also named EMIL HEITZ(1885), had been rector of Strassbourg Univer- After the war, he met ELISABETHSTAEHELIN (1896- sity.His father was a recognized Germanpublisher 1979) when both were students of biology at Basel Uni- (PAULHEITZ 1902).The family had owned the Strass- versity. HEITZmoved to Heidelberg and became a Ph.D. bourg University Press for generations (BURGUNand student of the plant physiologist LUDWIGJOST. Final RAY 1984). His own service as a volunteer and sergeant examinations were held June 7, 1921, and his thesis on with the German artillery during World War I was also divisionof chloroplasts came out the following year mentioned. As in many similar cases, the Minister for (HEITZ1922). He spent nine monthsas a postdoctoral Science, Teaching, and National Education made a fi- fellow at Tfibingen; during this time ELISABETHand nal decision in Berlin. According to $18 of the Imperial EMIL married. From June, 1922 to May, 1924, HEITZ Habilitation Rule (Reichs-Habilitations-Ordnungof De- was scientific assistant to FRIEDRICHBOAS, Institute for cember 13, 1934), HEITZwas to be removed from the Fermentation Physiology at Weihenstephan, Bavaria. A register of professors by August 17, 1937. His last salary further interval Uune, 1924 to September, 1926) was was to be paid in October of that year. spent at the Prussian University at Greifswald. There, This was a shock to a family with four children, RO- he not only did the job of a botanist but also took LAND (then 12years old), THOMAS(lo), ELISABETH (9) advantage of a working place at theZoological Institute and SEBASTIAN(4). Probably Mrs. ELISABETHHEITZ with PAULBUCHNER. (nee STAEHELIN)took the initiative to move to her Swiss Giving hisinaugural lectureon the problemof speci- native town Basel where her mother MARTHA STAEHE- ation on November 3, 1926, HEITZmade a splendid LIN-LINDERbought a house for the refugees. start in Hamburg. “It was here that he spent the most Fate and science: JOHANN HEINRICHEMIL HEITZ was fruitful 11 years of his scientific life” (Fa10 RESENDE his full name. He was born in Strassbourg on October 1962). 29,1892. In thefall of 1912he went to Munich where he At Basel University, he was also made an extraordi- attended 22 lectures on hereditary science by RICHARD nary professor for Botany. RESENDE visited him in 1938 GOLDSCHMIDT(1913). Two semesters (1913/1914) and “found out that his salary was less than that of a were spentat Strassbourg University. World War I tram conductor of that city. The situation improved (1914-1918) interrupted his course of studies. later, but was never very good.” LEWISJ. STADLER in- 12 H. Zacharias

was honorary professor of cytologyat Titbingen. He did not return toactive chromosome research but followed his interest in the ultrastructure of chloroplasts (HEITZ 1960). He retired on October 31, 1961, moved with his wife to Basel, and spentsome time in hissummer house, Cusn rossu. In 1962, he received honorary doctorates from the universities of Berlin, Cologne and Hamburg. EMILHEITZ died at Lugano, Switzerland, on July 8, 1965, as a result of a broken thigh bone, andwas buried in Basel.

Encouragement andinformation were given by WOI.FGASG0. Am. (Hamburg), HII.DEATZLIXR (Tilhingen), FRAWL BRARIX:(Hamhurg), HEINRICHEITZEN (Kid), JOSEF GREIIN (Wetzlar), EI.ISARF.TII GONTHER (Greifwald), El.lsAnETH H,\~S~:IITECI(~JLIN(;E:N(Zilrich), ROIAND HEITZ (Zilrich), MARION KALEMI (Berlin), ROIASD MAI.Y (Kriens), GEORGMEI.CI-IERS (Tilhingen), CIA’S PEI.I.ING (Tilhingen), GONTER RELITER (Halle), ARMIN SPILLER(Berlin), DAVID STADI.ER (Seattle), the lateESKO SUOMAIAINEN (Helsinki),Vrr TASE\WLI(Syd- ney), RAnA G. TEMIN(Madison). EWATHERMAN (Madison), RENATE UI.I.MANNnee DORMER(Ttibingen), and STEFANM’CI.F (Hamhurg).

LITERATURECITED BAIMANI,E. G., 1881 Sur la structure dunoyau des cellules salivaires chez les lames de Chironomus. Zool. Anz. 4: 637-641. BAUER,H., 1932 Die Feulgensche NuklealFirhung in ihrer Anwen- dung auf cytologische Untenuchungen. Z. Zellforsch. mikrosk. Anat. 15: 225-247. BAUER.H., 1933 Die wachsendenOocytenkerne einiger Insekten in ihrem Verhalten zur Nuklealfarhung. Z. Zellfonch. mikrosk. Anat. 18 254-298. FIGC:KI<3.-13111. HI

zweiundzwanzig Vorlesungen fur Studierende, Ante, Zuchter. 2nd ed. 480 in Bremische Biographie: 1912-1962, edited by W. LUHRS, F. Wilhelm Engelmann, Leipzig, Berlin. PETERSand K. H. SCHWEBEL.Hauschild, Bremen. Hamburg Staatsarchiv: Hochschulwesen, 1937 Heitz, Emil29.IO. 1892. KAUFMANN,B. P., 1931 Chromosome structure in Drosophila. Am. Dozenten- und Personalakten IV/384, Hamburg. Nat. 65: 555-558. HansischeUniversitit, 1936 Personal- undVwksungsuaeichnis: Win- KING, R. L., and H. W. BEAMS,1933 Somatic synapsis in Chirono- tersemester 1936/37, Sommersemester 1937. Universitit, Hamburg. mus. Anat. Rec. Suppl. 57: 89-90. HARWOOD, J.,1993 Styles of Scientijic Thought:The German Genetics KING, R. L., and H. W. BEAMS,1934 Somatic synapsis in Chirono- Community1900- 1933. University ofChicago Press, Chicago, mus, with special reference to the individuality of the chromo- London. somes. J. Morphol. 56: 577-591. HAUPT,G., 1932 Beitriige zur Zytologie derGattung Marchantia KOLTZOFF,N. K., 1934 The structure of thechromosomes in the (L.): I. Z. indukt. Abst. Vererbungslehre 62: 367-428. salivary glands of Drosophila. Science 80: 312-313. HEITL,E., 1885 Zur Gerchichteder alten Strassburger Uniuersitut: Rede, LE, M.-H., D. DURICKAand G. H. KARPEN,1995 Islands of complex gehulten am 1. Mai 1885, dem Stiftungstage der Kaiser Wilhelms-Una- DNA are widespread in Drosophila centric heterochromatin. Ge- uersitat zu Strassburg bei Antritt des Rectorats. Strassburg. netics 141: 283-303. HEITZ,E., 1922 Untersuchungen uber die Teilungder Chloroplasten nebst MELCHERS,G., 1987 Ein Botaniker aufdem Wege in die Allgemeine Beobachtungen uber Zellgrosse und Chromatophorengrosse: Inaugural- Biologie auch in Zeiten moralischer und materieller Zerstorung Dissmtation zurErlangung der Doktonuurde einer hohen naturwis- und Fritz von Wettstein 1895-1945 mit Liste der Verdffentli- senschuftlich-mathematischa Fakultat der Ruppecht-Karls-Uniuersitiit chungen und Dissertationen (Personliche Erinnerungen). Ber. zu Heidelberg. Heidelberg: Naturwiss.-math. Diss. v. 18. Marz 1921. Dtsch. Bot. Ges. 100: 373-405. Oscar Brandstetter, Leipzig. METL,C. W., 1916 Chromosome studies onthe Diptera, 11: the HEITL, E., 1926 Der Nachweis derChromosomen: Vergleichende paired association of chromosomes in Diptera, and its signifi- Studien uher ihreZahl, Grosze und Form im Pflanzenreich, I. Z. cance. J. Exp. Zool. 21: 213-280. Bot. 18: 625-681. METZ, C. W., 1926 Observations on spermatogenesis in Drosophila. HEITZ,E., 1928a Der bilaterale Bau der Geschlechtschromosomen Z. Zellforsch. mikrosk. Anat. 4 1-28. und Autosomen bei Pellia fabbroniana, P. epiphylla und einigen METL,C. W., and C. H. GAY,1934a Chromosome structure in the anderen Iungermanniaceen. Planta 5: 725-768. salivary glands of Sciara. Science 80: 595-596. HEITZ,E., 1928b Das Heterochromatin der Moose, 1. Jahrh. wiss. METZ, C. W., and C. H. GAY,193413 Organization of salivary gland Bot. 69: 762-818. chromosomes in Sciara in relation to genes. Proc. Natl. Acad. HEITZ,E., 1929 Heterochromatin, Chromocentren, Chromomeren Sci. USA 20 617-621. (Vorlaufige Mitteilung). Ber. Dtsch. Bot. Ges. 47: 274-284. MORGAN,T. H., 1919 The Physical Basis of Heredity. J. B. Lippincott, HEITZ,E., 1930 Der Bau der somatischen Kerne von Drosophila mela- Philadelphia, London. nogaster. Z. indukt. Abstammungs- Vererbungsl. 54: 248-249. MORGAN,T. H., 1921 Die stofpiche Cjrundlage der Vererbung:Vom Ver- HEITZ,E., 1931 Die Ursache der gesetzmaszigen Zahl, Lage, Form fasser autorisierte deutsche Ausgahe von Hans Nachtsheim. Bor- und Grdsze pflanzlicher Nukleolen. Planta 12 775-844. ntraeger, Berlin. HEITZ, E., 1932 Geschlechtschromosomen bei einem Lauhmoos MORGAN,T. H., C. B. BRIDGESand A. H. STURTEVANT,1925 The (VorlBufige Mitteilung). Ber. Dt. Bot. Ges. 50 204-206. genetics of Drosophila. Bihliogr. Genetica 2: 1-262. HEITZ,E., 1933a Die Herkunft der Chromocentren: Dritter Beitrag MUILER,H. J., and T. S. PAINTER,1932 The differentiation of the zur Kenntnis der Beziehung zwischen Kernstruktur und qualita- sex chromosomes of Drosophila into genetically active and inert tiververschiedenheit der Chromosomen in ihrerLangsrichtung. regions. Z. indukt. Abstammungs- Vererbungsl. 62: 316-365. Planta 18: 571-636. MULLER,H. J., and W. S. STONE,1930 Analysis of several induced HEITZ,E., 1933h Uber totale und partiellesomatische Heteropyk- gene rearrangements involving the Xchromosome of Drosoph- nose, sowie strukturelle Geschlechtschromosomen hei Drosophila ila. Anat. Rec. 47: 393-394. funebris (Cytologische Untersuchungen an Dipteren,11). Z. Zellf- PAINTER,T. S., 1933a A method for the qualitative analysisof the orsch. mikrosk. Anat. 19: 720-742. chromosomes of Drosophila melanogaster. Anat. Rec. Suppl. 57: 90. HEITL,E., 1934a Die somatische Heteropyknose bei Drosophila melanogaster und ihre genetische Bedeutung (Cytologische Untersu- PAINTER, T.S., 193313 A new method for the study of chromosome chungen an Dipteren,111). Z. Zellforsch. mikrosk. Anat. 20: 237- rearrangement and the plotting of chromosome maps. Science 287. 78: 585-586. PAINTER,T. S., 1934a A new method for the study of chromosome HEITZ,E., 1934b Uber a- und P-Heterochromatin sowie Konstanz und Bau der Chromomeren bei Drosophila. Biol. 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