304 Tlie American Naturalist. [April, 



apex of the embryo sac, covering the synergidac (fig. 37). In 

 some of the lower plants as Peronospora where the antheridium 

 develops a conjugating tube, a direct passage is said to be 

 formed by the bursting of the end of the tube which penetrates 

 through the wall of the egg cell (fig. 59). The further pro- 

 cess in flowering plants is, acccording to Strasburger, as follows: 

 The nucleus of the generative cell of the pollen grain passes 

 into the pollen tube and just before fertilization may be seen 

 in the apex of the pollen tube surrounded by protoplasm. 

 Before fertilization takes place this generative nucleus divides 

 into two nuclei (figs. 41 and 42) and one of these passes out 

 through the mucilaginous apex of the pollen tube and travels 

 between the disorganized synergidse to the oosphere. The gen- 

 erative nucleus then enters the oosphere, leaving behind it the 

 protoplasm which had served as a vehicle, and fuses with the 

 female pronucleus. Thus fecundation is completed and is as 

 we see by this outlined process, a fusion of nuclei which would 

 support the view that in reproduction the nuclei arc the all 

 important organs. The above description does not consider 

 the exisience of attractive spheres in the vegetable cell and as 

 stated in our consideration of cell division, Guignard, followed 

 by others, has lately asserted their universal occurrence accom- 

 panying the cell nucleus. 



Gui guard's Discoveries. 1 — After its introduction into the 

 pollen tube the generative nucleus is fusiform and surrounded 

 by a layer of differentiated protoplasm. The directive spheres, 

 two in number, are generally found at one end of the nucleus. 

 When the generative nucleus divides into two, as explained 

 above, after it has passed into the pollen tube and is located 

 near the apex, the longer axes of the nuclear spindle, is always 

 parallel to that of the pollen tube, hence that one of the result- 

 ing reproductive nuclei which is nearest the end of the tube 

 has its attractive spheres preceding it. While the other on 

 the contrary presents them behind the nucleus, where the 

 other pole was situated. Thus at the moment when the first^ of 

 these cells, which alone is charged with fecundation, penetrates into 



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