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Ovule, , Fertilization,Albumen: Confusion

* A. M. Showalter,Madison College, Harrisonburg,Virginia

The authordelineates what he considersthe currentconfusion as to the use of the termsindicated in the title. Downloaded from http://online.ucpress.edu/abt/article-pdf/28/8/645/26684/4441455.pdf by guest on 30 September 2021

Apparently there is much confusion and Dictionnairede la Langue Fran9aise(Littre) misunderstandingrelative to the reproductive definedthis term as: "nomdonne 'atort, chez processes in our common flowering . les plantesphanerogames, a l'6tat de la graine Much of this misunderstandingseems to be avant et pendantla periode de la floraison." attributableto the continueduse of outmoded = name given, erroneously as pertains to terms and discreditedconcepts in our teach- flowering plants, to the (primordium) ing. I was horrifieda few years ago when I before and during the time of flowering.] learnedthat an esteemedcolleague in my own Nearly all of the modern textbooks of gen- college was teaching his students that an eral or of general biology of my ac- is a little egg analogousto an ovum of quaintancegive fairly adequate descriptions an animal, that a grain is a male of the ovule as a complex structure,of which cell analogousto a , and that pollina- the chief constituent is a female sac tion is analogous to the fertilization of an containing successively a female sporocyte, animalegg. When I startedto offer corrective (4) female , an "embryosac" (really amendments,he stopped me with the remark a female )with a female , that the differenceis too subtle to be signifi- or egg; and later an embryonic cant to him or to his students. But a few as it becomes a seed. The serious deficiency hours of search in the library revealed the of many textbooks is in their failure to state appallingfact that the misconceptionsof my clearly or to explain adequatelythe essential colleague are currentin many otherwiserep- facts: (1) that the pollen grain is primarily utable publications,including some modern a spore, analogousto a spore of a , and dictionaries, both English and American, hence an infant (male) gametophyte, (2) some recent encyclopedias,some horticultural that the so-called "embryosac" is a female books, and even a few books of botany; al- gametophyte, (3) that fertilization is the though these concepts were discreditedmany union of an egg and a sperm (not the,union decades ago. of an ovule and a pollen grain, nor the Perhaps the following discussionwill help pollinationof a pistil), (4) that the meiotic some teachers of biology to a better under- divisionsof the sporocytesof floweringplants standing, and perhaps some teachers will (as of ), accomplish the formation of respect the idea that error is not sanctified haploid spores which are new individualsof by long prevailingusage. the gametophytic generation that live and The term "ovule"was introducedin 1808 grow as parasites within the diploid parent by the eminent French botanist, C. F. B. and form that accomplishsexual re- Mirbel. Originallyit meant "littleovum" and productionof new diploid and triploid (endo- was used in that sense for many decades in sperm) individuals. To replace the term French, English, and Americanbotanical lit- "ovule"with a more appropriateterm would erature. However, the 1873 edition of the probablyincrease the currentconfusion, but

645 to recognize the ovule for what it really is gamy" or "gameticunion"-which is highly and to teach accordinglyshould help to clar- commendable. ify the present confusion. ApparentlyAsa Gray was expressingthe Transeau and his colleagues pointed out best knowledge available to him when he many years ago that the term "ovulary"is characterizedpollen grains as "male genera- more appropriatethan "ovary"as applied to tive cells" and when (1858) he wrote "The floweringplants but, sadly, few writers have use of the pollen is to lodge on the followed their lead. Similarly "destaminate" of the pistil, where it growsin a peculiarway, seems more appropriatethan "emasculate" its inner coat projecting a slender thread though not in general use. which sinks into the pistil, somewhat as a The term "fertilization"is used indiscrim- growsdown into the ground,and reaches inatelyby many writers,including some high- an ovule in the ovary, causingit in some un- ly trainedbotanists, as applyingto any event known way to develop an ,and there-

or any process that contributesin any way by become a seed." Also when (1877) he Downloaded from http://online.ucpress.edu/abt/article-pdf/28/8/645/26684/4441455.pdf by guest on 30 September 2021 to the productionof offspring;from union of referredto the endospermtissue of a seed gametes, to penetrationof by pollen as "albumen"and likened it to the white of tubes, to pollinationof pistils, to enrichment a bird egg. But why the revisersof his Manual of soils. More discriminatingwriters define of Botany, up to the monumental8th edition and use this term as applying only to the of 1950, continue to use his outmoded ter- union of gametes,such as an egg and a sperm. minology and thus to perpetuatediscredited Some avoid the confusion by using "syn- concepts, is not apparent.

Newly Discovered Fossils tant to paleontologistsbecause this is the first solid evidence that these creatures existed A DartmouthCollege geological team has in the Precambrian geological period, the discovered720 million-year-oldanimal fossils Dartmouthscientist said. that may help clear up a mystery about how Most geologists believe that a sudden advanced forms of life evolved on earth. The change in the earth's physical environment fossils, found in the Canadian arctic, are at took place about 600 million years ago, he least 120 million years older than any ad- said. Biologists feel that the earliest animals vanced forms known to paleontologists. with specialized organs and tissues could There, in an unaltered group of Precam- have developed only after oxygen became brian sedimentaryrocks in the Shaler Moun- plentiful in the air and oceans. With abun- tains, unique because they were little dant free oxygen possibly created by more changed by the pressuresof mountainbuild- abundant life, they suggest that an ing or the weight of overlying rocks, they "evolution explosion" occurred and many found fossilized remains of brachiopods. types of quite advanced animal life seemed They also turned up several kinds of fossil- to appear quite suddenly. ized tracks and trails made by burrowing In the ordinarycourse of evolution, these wormlikeanimals and small tubes and spines advancedforms of life would seeminglyhave of an as yet unknown species. to evolve from earlier, fairly complex crea- tures. But previouslythere was no fossil evi- The test results, by radiocarbon dating, dence to support showed that the fossils are this. at least 720 mil- The party's lion years old and may be considerablyolder. findings appear to constitute a The previously generally accepted date for breakthroughin our knowledge of life dur- ing the earliest, the beginning of advanced forms of life on very long periods of geo- logic time. They push back the known dates earth was about 600 million years ago. of more advanced forms of animal life by at The discoveryof the brachiopodsis impor- least 120 million years.

646 The American Biology Teacher, October, 1966