THE ANGIOSPERMAE 



1425 



Fig. 13 1 5. — Trapella sinensis. A, Young embryo sac with 

 three unde\eloped megaspores below. B, Later stage 

 with young embryo in the sac. The lowest megaspore 

 divided and forming a chalazal haustorium. The per- 

 sistent svnergidae shown above the embr\o sac. 

 {After Oliver.) 



These latter cases are perhaps better classed with the " basal apparatus ", 

 which Schiirhoff described as being formed within the embryo sac, either 

 by the concentration of a mass of cytoplasm and endosperm nuclei at the 

 antipodal end or by the development of an aggressive basal cell, in endo- 

 sperms of the Helobial type (see p. 1453), which may divide or become multi- 

 nucleate and sometimes forms a haustorium into the chalaza. 



That all these types of structure are of similar physiological importance, 

 which can hardly be other than nutritive, is shown by their mutual exclu- 

 sion or vicarism. Thus in Ranunculaceae, etc, where the antipodals are 

 markedly developed, there is no endospermal basal apparatus. Where the 

 endospermal basal apparatus is most striking (Juncaceae, Helobiae, etc.), 

 the antipodals are small and evanescent. 



Haustorial outgrowths of the embryo sac itself, in the form of caeca or 

 diverticula, are in a different category from those produced by the antipodal 

 cells, for they may be formed at various parts of the embryo sac and they 

 may, or may not, involve the antipodals, they may indeed be formed where 

 no antipodals are present. A simple diverticulum is formed laterally from 

 the embryo sac of Agrostemma githago and other members of the Caryo- 

 phyllaceae. It may become nearly as large as the parent sac and penetrates 

 the fleshy mass of tissue which is partly funicle and partly integument. The 

 antipodals are evanescent and are not involved, but one of the two primary 

 endosperm nuclei moves into the outgrowth, which persists as a remnant 

 into the ripe seed, although containing very little endosperm. Similar lateral 



