THE SEED PRODUCTION OF PIN US SYLVESTRIS. 23 



cavity above the neck cells. The sperms when initiated 

 are about 15 microns in diameter ; they grow rapidly, 

 reaching maturity and a diameter of 28 microns to 30 

 microns before they have left the spindle. 



Before proceeding to describe the act of fertilisation, 

 it will be well to refer to one or two points of some 

 importance. First with reference to the division of the 

 generative cell. Dixon gives the time at which this occurs 

 as towards the end of April, and as he found fertilisation 

 took place at the end of May, the division was just a month 

 before that event. Margaret C. Ferguson, in her 

 exhaustive and accurate work upon P. strobus says that in 

 P. strobus and P. austriaca " the stalk and the generative 

 cell (body-cell) are formed as a rule before the approach 

 of winter." That is during the second season. From the 

 many preparations I have examined, I conclude that 

 Dixon was quite right with regard to P. sylvestris, but his 

 statement that very shortly after this the body cell divides 

 within the grain — he so figures it — to produce the two 

 sperms, I cannot confirm. I also think the dates given by 

 him for the various phases are open to question : it looks 

 as though he had got his material mixed. 



The next point refers to the " proteid vacuoles. " 

 "Whence come they ? Without doubt they are derived 

 from the jacket cells, which enclose the egg on every hand. 

 It is the function of these cells to provide the food 

 necessary to the growing egg. This is accomplished by 

 their protoplasmic contents becoming reduced to a finely 

 divided granular condition ; in this state it passes through 

 the perforated walls of the cells into the egg. The 

 perforations are comparatively large and easy of demon- 

 stration, an aqueous solution of saffranin differentiating 

 them quite strongly (fig. 7). Owing to the slight 

 shrinkage of the egg cytoplasm, which generally occurs 



