Page:The New International Encyclopædia 1st ed. v. 10.djvu/54

* HETEROPODA. 40 HETEROSPORY. and OxypjTus. have delii'iiU- invulutc shells. These reseniblc in soiiio i"t'S|H"els those of certain fossil Bollerophons of Paleozoic age, and the rcscm- hlaiu'o has led many authors to include the liel- lerophontidtr with the Heteropoda in spite of their larger size, and heavier and thicker shells. fcjeo IJKI.I.KHIU'IION ; (lASTUOl'OD.V. HET'EROPTERA (from Gk. erepot, heleros, other + -Ttpbv, plcroti, wing). A suborder of the Heniiptera, including the •true' hugs, eliar- acterized l>- dissimilarity in the wings. The proximal half of the anterior pair of wings is thickened, much like those of beetles. The stib- order inchuU-s a number of aipiatic forms, some of which occur out at sea hundreds of miles from land. The water-boatman (Corixa undulata), with a pair of oar like legs, the large water- bug or •electric-light bug' {Belostoma Ameri- itiuiim). anil the hmg-legged water-st riders are, perhaps, the l)est known of the aquatic forms. The bedbug, redbug. chinch-bug, squash-bug, and stink-bugs (qq.v. ) are other familiar and impor- tant Heteroptera. See llEMtPTKRA; IIOMOITERA. HET'EROS'POBY (from Gk. Irepot. heieros, other + cTrdpot. sporos, seed ) . The production, by plants, of two kinds of se.xless spores. Heter- cspory is one of the most important phenomena in connection with the evolution of the plant king- dom, since through it the seed has appeared, and since a clear concc|)tion of (lowering plants is im- possible without s(mie knowledge of the begin- nings of heterospory. The phenomenon ap|ieara first, and in its simplest form, among certain of the fern-plants ( Pteridophytes). and is universal among the seed-phuits ( spcrniatophytos). To un- derstand the significance of heterospory it will l>e necessary to read the article on .r.Ti;RNATloN OF Generations, since this deals with the two kinds of spores produced by the sexless genera- tion ( sporophyte ). 'microspores.' More important than the fact of dificrencc in size, however, is the other fact that the micros|>ores produce sexiuil plants which bear only male organs, and the megaspores sexual plants which bear only female organs. There is a very definite relation between tlie amount of nutrition and the appearance of the female organs, so that the larger and hence bet- ter-nourished spore is cx|K-ctcd to produce a fe- male plant. In consequence of heterospory. therefore, the sexual plants become distinctly male and female. The unfortunate thing is that the sexual character has often been applied to the microspores and the UH'gaspores. which are simply the sexless spores of a sporophyte, which necessarily produce gametophytes. BETER08P0BY. MegasporaDglum of a club-moss coDtalnIng four mpga- Bpores. In ordinary ferns the spores are alike, and in germination each one produces a sexual plant (gametophyte), which bears both the male and the female sex organs. Such a condition is called 'honiospory' (q.v. ) or 'isospory,' which means in each case 'spores similar.' Wry gradually the spores begin to differ in size, until presently some become very much larger than others. The large spores are called 'megaspores' and the small ones HETEBOBPOBY. Mlcrosporangium of a chib-moes containing numerous microspores. When spores become thus differentiated in size and in product, the spore-cases (sporangia) are also differentiated, so that certain sporangia produce onlj' microspores, and others produce only megaspores. The former were naturally called 'microsporangia' and the latter 'mega- sporangia.' These sporangia are ordinarily pro- duced upon leaf-like structures, and later the leaves hearing sporangia become differentiated in the same way, so that certain leaves bear only microsporangia and other leaves only mega- sporangi.a. Naturally the former were called 'microsporophylls' and the latter 'megasporo- phylls.' These names are used in connection with those fern-plants which are heterosporous, as the water-ferns, the little club-mosses (Sela-* ginella), and the quill worts (Isoetes). Among the .seed-plants ((lowering plants), however, the corresponding structures already possessed names long in use, and not to be discarded. It is impor- tant, however, to know the structures among the seed-plants that correspond to tho.se among the heterosporous fern-plants. It is found that the stamen (q.v.) of a flowering plant is a micro- sporophyll, that its pollen-sacs are microspo- rangia. and that the pollen-grain is a miscrospore. 1'he interesting conclusion is reached, therefore, that the pollen-grain is a sexless spore, a conclu- sion quite contrary to the general impression that it is a male cell, and that the stamen is a male organ. It is found that the carpel (q.v.) of a flowering plant, which organizes the ovary, style, and stigma, is a megasporophyll ; that the ovules are megasporangia ; and that the so-called embri^o-sac is a single large unshed megaspore. It follows, therefore, that the o^Tile is by no