54 MARGARET C. FERGUSON 



true sequence of events in the development of the pollen-tube. 

 When once the mitotic figure was observed in the -pollen-tube^ 

 scarcely more than a week before fertilization , and the fact 

 noted that special staining was necessary in order to study this 

 mitosis satisfactorily, further research was prosecuted with 

 comparative ease. I find no authority in Dixon's paper for the 

 statement recently made by Coulter and Chamberlain ('01) 

 which reads as follows: "The liberation and descent of the 

 body cell into the tube," etc., " has recently been described in 

 detail by Dixon." What Dixon ('94) does affirm is this : "Very 

 shortly after this it is found that the body-cell has broken free 

 from the stalk-cell and has divided into two cells, which are 

 almost equal in size. These cells are the male sexual cells. 

 During this process the wall of the stalk-cell is ruptured and its 

 nucleus follows the two cells resulting from the division of the 

 body-cell which move into the pollen-tube." And throughout 

 Dixon's paper there is no sentence that could be interpreted as 

 implying that the body-cell ever passes into the pollen-tube 

 before dividing to form the male sexual cells. 



After the generative cell has passed into the pollen-tube but 

 while it is still in the upper dead portion of the nucellus, it gives 

 rise to the sperm-nuclei by a division which presents some new 

 and interesting features, although it resembles to a greater or 

 less degree certain mitoses described by various cytologists 1 

 during the past few years. 



When the generative nucleus has again come to lie in the 

 extreme upper portion of its cell, certain changes in the cyto- 

 plasm indicate that division is being initiated. At some little 

 distance below the nucleus the cytoplasm shows a finely granu- 

 lar structure which is not at this stage dense nor deeply stain- 

 ing. From this region irregular granular threads arise which 

 extend outward towards the periphery of the cell, those extend- 



1 Of the long list that might be mentioned I have noted only the following : 

 Rosen ('95) in the root-tip of hj-acinth ; Osterhout ('97) in Equisetum" Swingle 

 ('97) in SphacelartacccE ; Schaffner ('98) in root-tip of Allium Cepa ; Mottier 

 ('98) in the embryo-sac of Liliumj Fulmer ('98) in pine seedlings: Hof ('98) 

 in Ephedra and other plants; Nawaschin ('99") in Plasmodiophora ; Nemec ('98 

 and '99) in various plants; Strasburger ('oo) in Vicia Faba ; Mottier ('oo) in 

 Dictyota; and Murrill ('oo) in Tsuga. Of animal cytologists I mention but 

 one, Hertwig, R. ('98) in A ctinospk cerium. 



