33° 



MORPHOLOGY OF GYMNOSPERMS 



The archegonium initials become recognizable at various stages 

 in the development of the gametophyte. In Taxus and Torreya 

 they appear as soon as the sac is full of tissue; in fact, any earlier 

 differentiation would occur in the stage of free nuclei and would 

 result in the selection of eggs and the elimination of archegonia. This 

 tendency to differentiate the female sexual organ earlier and earlier 

 in the history of the gametophyte has been 

 referred to under Pinaceae (p. 263) ; and in 

 this feature Taxus and Torreya stand in an 

 extreme position. In Cephalotaxus (124), 

 on the other hand, the archegonium initials 

 do not appear until the endosperm is well 

 developed; and in Podocarpus the gameto- 

 phyte is two-thirds to three-fourths its full 

 size when fertilization occurs. In some 

 cases, therefore, the principal growth of the 

 endosperm takes place after fertilization, 

 and in other cases before fertilization. 



The development of the archegonium is 

 exactly as described for the Pinaceae (p. 263), 

 and no archegohial complex is formed, each 

 archegonium having its separate chamber 

 and jacket (in case there is one). In 

 Phyllodadus occasionally two archegonia 

 occur in a common jacket (174) . The arche- 

 gonial jacket, investing the central cell and 

 later the egg, is not developed so constantly 

 or so conspicuously as among the Pinaceae. 

 In Phyllodadus (144) it is conspicuous, , 

 consisting of a layer of cells with large 

 nuclei or several nuclei; in Cephalotaxus (124) it is less con- 

 spicuous, frequently being interrupted by ordinary cells; while 

 in Torreya (loi) it is not evident until after fertilization and is 

 then weakly organized. The condition of this jacket among Tax- 

 aceae is not known well enough to justify a general statement, 

 but among the taxads, at least, it gives the impression of a vanish- 

 ing structure, which finds its parallel in the disappearance of the 



Fig. 381. — Taxus bac- 

 cata: eight-nucleate stage of 

 female gametophyte; X37S. 



— ^After STRASBtrRGER(lOo). 



