52 MARGARET C. FERGUSON 



later in the egg. During the time that this cell is moving over 

 the generative cell its cytoplasm cannot always be differentiated 

 from that of the latter ; but when once the stalk-cell has passed 

 the generative cell, its nucleus surrounded by a sphere of very 

 vacuolate cytoplasm, scarcely more than a peripheral layer, is 

 again distinctly demonstrated (figs. 90 and 91). After pass- 

 ing the generative nucleus, the stalk-cell ordinarily takes up 

 a position between the generative cell and the tube-nucleus 

 (fig. 92), but occasionally it may pass the tube-nucleus (fig. 

 93). This phenomenon is always accompanied by a great in- 

 crease in the starch content of the pollen-tube, the tube being 

 in some instances almost filled with starch in the region of the 

 generative cell (fig. 91). 



When the generative cell leaves the pollen-grain, its nucleus 

 is situated near the top of the cell, but the nucleus of this cell 

 evidently moves faster than its cytoplasm, and at the time when 

 the stalk-cell is passing over the generative nucleus this nucleus 

 has come to lie at or below the center of its cell (fig. 84, 90 

 and 91). Shortly after this the generative nucleus is again 

 observed at the uppermost part of its cytoplasm. 



During its passage into the tube, the generative cell increases 

 much in size ; it has no definite cell-wall, and its cytoplasm forms 

 a large, irregular tongue about the nucleus. This cytoplasm in 

 no way suggests the alveolar structure of Butschli ('94) but is 

 distinctly reticular, differing in appearance from the nuclear 

 net only by its greater delicacy. This is shown more clearly 

 at a somewhat later stage. 



The tube- and generative nuclei are now very similar in 

 structure, though each is sufficiently characteristic to be readily 

 recognized by one who is familiar with them. The tube-nucleus 

 has one large, usually homogeneously staining nucleolus, rarely 

 one or more smaller nucleoli, and it is furnished with a rather 

 scanty, delicate reticulum which is apparently poor in chromatin. 

 Either it is in a state of partial collapse, or, what is more prob- 

 able, it is very hard to fix at this period in its history, for its 

 outline is, as a rule, quite irregular at this time. The genera- 

 tive nucleus has one large, hollow or vacuolate nucleolus, and 

 commonly two smaller ones; its reticulum, though more abun- 



