134 MARGARET C. FERGUSON 



mitotically. I have only three times observed an excess of the 

 normal number of nuclei in the male gametophyte of Pinns. 



Three nuclei have been found in the pollen-grain after the tube- 

 nucleus has passed into the pollen-tube (tig. 271, plate XXIV). 

 Two nuclei have twice been seen just passing into the pollen- 

 tube, while the stalk-cell could still be detected in the lower 

 part of the pollen-grain in one instance, and in the other it had 

 just left the grain but had not as yet passed the generative cell. 

 In the former instance (fig. 272) the stalk-cell was almost 

 obscured by the dead nucellar tissue and is not shown in the 

 sketch. Here the two nuclei are in close contact, the smaller 

 nucleus being imbedded in one side of the larger nucleus. In 

 the second case (fig. 273) the nuclei are farther removed from 

 the pollen-grain, although still connected with it by the cyto- 

 plasm of the larger cell ; the smaller nucleus is surrounded by 

 its own cytoplasm and is in contact with the lower part of the 

 larger cell. 



An}^ interpretation of these irregularities must be more or less 

 hypothetical, and yet from the position, size, and structure of 

 the nuclei certain inferences can be made regarding them. In 

 the condition represented in fig. 271, one of the prothallial cells 

 may have persisted, the stalk-cell may have divided, or the 

 generative cell may have given rise to the extra nucleus. But 

 considering the character of the nucleus and also that of the 

 nucleus of the stalk-cell, it seems to me most probable that two 

 stalk-cells have been formed. In figs. 272 and 273 the proba- 

 bilities are very strong that the smaller nucleus in each instance 

 was cut off from the generative nucleus. The stalk-cell is per- 

 fectly normal in appearance and gives no evidence that it has 

 passed through any unusual history. The two large nuclei 

 shown in fig. 273 bear a very striking resemblance to the 

 sperm-nuclei, and when first observed with a lower power of 

 the microscope the impression was that the generative nucleus 

 had divided very early and the smaller sperm-nucleus was in 

 advance. But, when the higher magnification revealed the 

 stalk-cell still above these nuclei, and also disclosed the fact that 

 there were in reality two cells, it at once became apparent that 

 these are not to be considered sperm-nuclei. For two sperm- 



