472 THE BOTANICAL MAGAZINE. [vol. LI, No. 606. Fig. 9. Die zusammengesetzte Konvektion aus Wasserflachen von im hexagonalen drei- zeiligen Kontakt gestellten 1.9 Flaschen. Durchm, der Flasehe 3.7-3.8 cm, der (Tel Offnung 2.3-2.4 cm, t 14.1°, wt 19.7°, t' 10.9° (=63%). 2.3-2.4 cm. t 14°.1, wt 19°.7, t' 10°9(=63%). Fig. 10. Verhinderung des Rauchstromes lurch Drahtnetz, x ea. 1/9. a. Per eben abstromende Ranch mit pilzformiger Front. b. Der fiber deco Netz rich verbreitende Ranch; nur am mittleren Teile beginnt der Ranch durch das Netz hindurchzustromen. Das Netz ist aus Kupfer- drraht von 0.3 mm Durchm., seine Masehenzahl betragt 60 x 64/10 em. t 25.6°. e. Der Strom hat sich noch welter verbreitet, teils wieder hlndurchstromend. The Origin of Najas and Potamogeton. By Shigeru Miki. With 1 Plate and 3 Text-figures. ReceivedMarch 31, 1937. Introduction, It is a well known fact, that in water plants the reduction and simpli- fication of floral parts occurs very frequently probably in accordance with their aquatic habit. Najas and Potamogeton, both of which have apetalous flowers, are considered generally, merely on account of that fact, to be closely related. A closer examination shows however that the floral scheme is not similar. The flower of Potawogeton should be interpreted as a reduced inflorescence, so that it is nearly related with Synanthae or Pan- danales, while Na jas may be considered as a descendant of the ancient stock of submerged Ilydrocharitaceae. I wish to express here my sincere thanks to Prof. K. KOIiHA under whose direction and by whose courtesy this study was undertaken. Historical. Najas and Potainogeton are regarded usually as a descendant of a trimerous monocotyledonous ancestor, CAMPBELL(4), however, considered the group to be related to the heterosporous Filicales, especially with Isoetaceae. The affinity of Najas is, owing to the extremely simple flower, quite obscure, so that there are a number of opinions. MAGNus(15) regarded - 290 - Shibata Commemoration Article, 40 Juue20,1937.1 ~. MIKI-ORIGIN OF NAJAS AND POTA]10GETON. 473 it to be related to Zannichellia, CHRYSLER(S) suggested its development from Potamogeton through Zannichellia, HUTCIIINsON(12 ) considered Naj a- dales including Cymodocea, Diplanthera, Althenia, Zannichellia and Najas to be derived from Alismatales. Both genera are included in Helobiae by ENGLER(8), LoTsY(14), RENDLE(24) , WETTSTEIN(28) , IIUTCIIINSON (12) , MARKGInu (16) and others, but KORIBAand MIKI(13) Suggested the genus Potamogeton based on some allied fossil remains, to be connected with Spadiciflorae. Na jas. a. Character. Morphological characters are well known after MAGNUS(15) and ot!lers(3). At a glance the shoot seems to have dichotomous branches and a 3-whorled arrangement of leaves except Najas gracillima (A. Bn. ) MAGNUS(Pl. X, A). This features is derived from the mode of growth, that the monopodial shoot has apparently opposite leaves, the lower one of `Which produces a lateral shoot and one or three flower buds in the same axil, and the 1st or 3rd leaves on the lateral shoot are attached sessile and tra.us- versal. Subgenus Ennajas has epidermal cells, distinctly smaller than the cortical cells, but in subgenus Can linia they are entirely undifferentiated. The vascular bundle of the shoot is central, and the lacunae in the cortical part; the crystal of calcium oxalate is absent throughout the shoot-tissues. The flower is monoecious (Subgenus Caulinia) or dioecious (Subgenus Eunajas) withoutt scape; the female flower is usually solitary, but there aie two in Najas gracillinia (A. BR.) MAGNUS(Pl. X,D), and without spathe except Section Spat haceac. The one-celled ovary has an anatropous ovule and thread-like stigma, separated into 2 or 3 parts. rl'he male flower iw enclosed in a bottle-shaped spathe except the Section Nudae. Anther 1- -1-celled;the anthesis occurs outside of the spathe by elongation of the pedicel (P1. X, B-C'). The shape of pollen is usually oblong with single uncuti- cularised membrane. Fruit and germination. The seed separates easily from the carpel, and has characteristic areolation on the epidermis of the testa; and macro- podous embryo contains large starch grains. Germination is epigeous and the seedling has a primary root. b. Coiisideration of Characters. Ecological. Najas is highly adapted to aquatic life as may be seen from those characters mentioned below: the undifferentiated epidermal cells, the single uncuticularised pollen membrane, the reduced development 291 -- 474 TILE BOTANICALMAGAZINE. [x'01.LI. No. 606. of roots in contrast with densely branched shoots. The verticillate leaves seem also to be associated with stagnant water, just as are those of Ambulia, Hydrilla, Ceratophylinn and others. It grows usually in a shallow pond or lake laid in alluvial plane, where seasonal flood can easily take place. The delicate shoots of these submerged plants then separate easily at their nodes and flow away, whereas those tightly fixed water plants such as Nyniphaeaceae and others are deprived of light and ultimately are ruined. After this habit they may be called "semifloating plants." Morphological. The absence of scape under the flower seems to be associated with the erect habit of the shoot as in Ilydrocharitaceae, while those water plants with tufted shoots as Vallisneria, Blyxa and Ottelia have an elongated scape. The production of flower acid lateral shoot froi:~ the same a~~ilJis quite peculiar, though common in Ilydrocharitaceae. Therefore it seems to be more reasonable to conceive that Na jas has also an intimate affinity with Ilydrocharitaceae. The spathe is considered as the outer perianth by MAGNUS,but it is really a spathe, because the male flower elongates and is lifted out of this organ before dehiscence as in P1. X, B, C and C'. On the contrary, the envelope of the male flower, the membranaceous envelope of the anther, which was once supposed by CAMPBELLto be analogous with the integument,, is really a perianth. One-celled theca seems to be derived from the usual four-celled one, as has already been stated by many authors. The perianth of the female flower is entirely absent, though in some species as Na jas f oveolata A. Bra. (Pl. X, E) a slight indication may be seen at the lower part of the stigma as an annular swelling. The flower is. suggested therefore to be epigynous. c. Relationship. RENDLEnoted that the character of the vegetative part of Najas is nearly the same as submerged Ilydrocharitaceae, but still he regarded it to be a primitive type of Monocotyledon. Not only the vegetative characters, but also their reproductive organs, even if simplified, are alike in these two groups, though they show at the same time marked contrasts with those of Potamogeton as tabulated below (next page) The probable course of the simplification of Na jas from the submerged Ilydrocharitaceae is shown in Fig. ].. Najas shows also an intimate relation to Zannichelliaceae (Fig. 2), especially in the elongated pedicel of the male flower, some of which have reduced perianth as Alt henia(22) and Diplanthera(18). All these charac- ters show, however, marked contrasts with Potamogeton.. The distichous. - 9Q9 - June 20,1.937. l S. ]II KI-ORIGIN OF NA JAB AND POTAMOGET ON. 475 Fig. 1. Relationship of Na jas with submerged Hydrocharitaceae in contrast with Potamogeton (somewhat diagrammatic). A. Elodea. B. Hydrilla. C. y'allisneria. D. Na jas. E. Potamogeton : 1, Subgenus Eupotamogeton, 2, Subgenus Coleogeton. W. Water surface. 511. Shoot (aaillary buds are omitted). F. Floral diagram. F'. Diagram of flower bud and lateral shoot. P0. Pollen, a. main axis. p. peduncle. s. spathe. (The shoot of Vallisnei°ia is drawn here diagramniatically, as the lateral branches develop after every three consecutive leaves as shown in Pl. X, F). - 293 - 476 THE BOTANICAL MAGAZINE. [ vol. LI, No. 606. or axillant leaves on the lateral branches of Potamogeton, though they are similar to sea-grasses viz. Gym.o- clocea and Diplanth,era (17, 18) of Zalinichel l la- eeae and Tlzalassia of Ilydrocharitaceae, may be associated with their specific habitat, namely with the movement of water in the sea. d. Birthplace. The original home niay be tropical, prob- ably in Africa, where also occur various primi- Fig. Relationship of Najadaceae and ZanlliehCl- tive sections of Spatha- llneene (some«'liat dlagramniatie 1 ceae and many allied A. Na jas. ID. Zoo nichellia. C. Alfhenia (F ,after ~CHUmIANN,F' and P after PRII.LIEUX). I). Dirilan- species of Zannicliellia theia. E. Cyinodocca (F, F' and P after Boi;xicr). Aschersoniana GRAEn. F. Staminate flower. PD. Pollen. F. Transverse sec- tion of staminate flower, S. Diagram of flower and (2), Althenia and sub- lateral shoot (hlack circle). p. perianth, nI. main merged If ydrocharita- axis. ceae. Potaroget®nt a. Character. A shoot wiPi alternative leaves except those of spike and of Section Densi. Sympodial rhizome is composed of the basal two nodes of the lateral shoot. There are sheathing leaves at least in its early stage. The shape of the epidermal cells of floating leaves are long and narrow. The vascular bundle in the peduncle or stem is usually separated, except sub- genus Coleogeton. Crystals of calcium oxalate are not present. The flower Oil the spike-like inflorescence, is sometimes reduced to one as in the submerged form of Potamogeton Spirilins TUCKERMAN(9) . Pistil 4 (1-8) enclosed within 4 scale-like bracts, 2-celled extrorse anther attaching to each side of the stalk, except subgenus Coleogeton (Pl. X, J). The pollen is round or oblong. The development of the embryo sack is the -- 294 -- June 20, 1937.] S. MIKI-ORIGIN OF NAJAS AND POTAMOGET ON. 477 normal type (11, 29).