SPERM \ TOIMIYTES 215 



consisting usually of two (fig. 478) or three cells, but in Podocarpus 

 it sometimes becomes a mas>i\c structure of about twenty-five cells. 

 There is no well-defined archegonial jacket, and when it is remem- 

 bered that there is no special digestive zone about the mother cell, 

 it is evident that the nutritive mechanism is not differentiated in 

 this group as it is in Ginkgo, or even in the cycads. In the division 

 of the nucleus of the ventral cell, which precedes the formation of 

 the egg, there is no separating wall formed, and hence no ventral 

 canal cell. The ventral nucleus is its only representative, and in 

 Torreya it is doubtful whether even this 

 appears. The disappearance of the ven- 

 tral canal cell and its nucleus is the last 

 stage in the reduction of the axial row, 

 which thereafter is represented only by the 



egg- 

 Male gametophyte. — In the development 

 of the male gametophyte, the podocarps and 

 taxads show a striking contrast. In the FlG 4?8 y 0U ng arche- 



podocarps two to six vegetative (prothallial) gonium of Torreya, showing the 



cells appear (fig. 480); while in the taxads two neck , cells * nd the centra ! 

 . ,7 I 1 i- , cell. — After Coulter and 



no vegetative cells have been discovered. l and . 



The division of the generative (primary 



spermatogenous) cell into the sterile stalk cell and the body cell is 

 as described for the preceding groups (fig. 480); but a striking change 

 appears in the fact that there are no blepharoplasts in the mother 

 cell, which means that ciliated (hence swimming) sperms are not 

 formed. The nucleus of the body cell divides, and this division may 

 be accompanied by a separating wall, so that two sperm mother 

 cells are formed (taxads); or the nuclear division may not be accom- 

 panied by wall formation, so that there are only two mother cell nuclei 

 in the general cytoplasm of the body cell (podocarps). In either case 

 the division is unequal, so that only one cell or one nucleus functions 

 (fig. 479). No sperms are formed, but the mother cell functions directly 

 as a sperm, its nucleus being the structure essential in fertilization. It 

 has become the habit to call these mother cells that do not form sperms 

 internally and discharge them, but function themselves as sperms, 

 simply male cells. 



Fertilization. — In pollination (by the wind) the pollen grains come 

 to rest on the tip of the nucellus, and in the absence of a pollen chamber 





