CONIFERALES 85 



the time of the cutting off of the neck cell to the cutting off of 

 the ventral canal cell, a period of two or three weeks, beginning 

 between the middle of May and the 1st of June, dependent on 

 the season. The central cell now begins to receive supplies from 

 the jacket cells, which practically empty themselves through the 

 pits. As a consequence, the central cell becomes packed with 

 food material, the cytoplasm being filled with large and deeply 

 staining masses, even more prominent in the egg, the best organ- 

 ized of which have been called " proteid vacuoles." These " vac- 

 uoles " of the central cell and egg were regarded by Hofmeister 

 and Goroschankin to be nuclear structures, but Strasburger de- 

 nied their nuclear nature, and claimed that they are proteid 

 vacuoles, and such they have been regarded ever since, until the 

 recent investigations of Arnoldi. 43 He observed that the nuclei 

 of the jacket cells become amoeboid, squeeze through the pits, 

 and regain their form in the central cell and egg. Xuclei were 

 also observed to pass from the next outer layer into the cells of 

 the jacket. In addition to these organized nuclei, nuclear frag- 

 ments and other materials pass in from the jacket cells, which 

 may often be seen emptied of their contents. 



The cutting off of the ventral canal cell has been known in 

 a general way since Strasburger 24 established its existence in 

 Juniper us. The fullest accounts, however, have been given by 

 Blackmail 37 and by Chamberlain. 39 Just before fertilization, 

 which we find in Pinus Laricio to occur about the 1st of July, 

 the ventral canal cell is cut off (Fig. 64, D). A broad spindle, 

 which is almost rectangular in outline before it becomes bipolar, 

 is organized at the apical extremity of the central cell, and there 

 appears a thin but broad and sinuous cell plate. This cell plate 

 cuts out from the main mass a small oval segment, the ventral 

 canal cell (Fig. 65). After the separation of the ventral canal 

 cell, its nucleus begins to return to the resting stage, but accord- 

 ing to Blackman it never reaches it before disorganization sets 

 in. After this the ventral canal cell appears in various stages 

 of disorganization, often separating somewhat from the egg, and 

 has usually disappeared by the time the pollen tube has pene- 

 trated the neck of the archegonium, although Chamberlain 

 found occasional traces of it even after the embryo was con- 

 siderably advanced. 



Blackman noted the exact similarity between the nuclei of 



