EVOLUTION OF ANGIOSPERMS THROUGH APOSPORY 1 77 



of the cycads and coniferce. It is not built up before fertiliza- 

 tion takes place, but afterward. It does not arise from a ger- 

 minating spore, but as a result of the conjugation of two nuclei, 

 comparable, perhaps, to the conjugations of adjoining cells 

 which occur in the prothallia of certain ferns and give rise to 

 the new double-celled structural phase by apogamy without the 

 production of antheridia and archegonia, as though the ancestral 

 form had all the liberty of alternatives possessed by the ferns 

 and had ended by combining them into the complex and hitherto 

 altogether mysterious reproductive processes of angiosperms. 

 The part of the angiosperm which, in the present view, might 

 correspond to the prothallus itself, is the nucellus. And even 

 this relation would not be direct, for the nucellus of the angio- 

 sperms might not be homologous with the nucellus of the coni- 

 fers and cycads, which, if current interpretations are correct, is 

 more analogous to the placenta of the mammal than to an apos- 

 porous prothallus. 



The obviously very great and fundamental difference between 

 the angiosperms and gymnosperms would be adequately ac- 

 counted for. The homologies which have been alleged hitherto 

 appear very artificial, and leave us with a problem as difficult 

 as that which they are intended to solve, namely, how structures 

 derived from those of ferns or of gymnosperms could have 

 become so completely different in the angiosperms. 



VEGETATIVE PARTS REPRESENT STERILIZED REPRODUCTIVE 



TISSUES. 



The deduction based by Bower on his studies of fern-struc- 

 tures would remain thoroughly applicable to the angiosperms, 

 since their vegetative parts would still represent sterilized repro- 

 ductive tissues. Indeed, this proposition becomes a mere truism 

 after the essentially sexual nature of the double-celled struc- 

 tures of the higher plants has been realized. The growth of 

 the whole plant body has been intercalated into the sexual 

 process. It is built up during conjugation and not after conju- 

 gation has been completed.' 



'Cook, O. F., and Swingle, W. T., 1905, Evolution of Cellular Structures, 

 Bui. 81, Bureau of Plant Industry, U. S. Department of Agriculture. 



