334 NINETEENTH REPORT. 



division follows immediati'ly^ a spindle being observed about May 25, 

 (Fig. 16-H). This division is a repetition of the first in details and the 

 two lenticular cells disorganize rapidly, (Fig. 16-1), become flattened 

 against the spore wall, and very soon appear merely as two thin and 

 deeply staining disks, which are overgrown rapidly by the intine. * * * * 



"The third (large) cell, which is a sister to the second evanescent vege- 

 tative cell, is an antheridial cell in the sense that it gives rise to a series 

 of cells which represent the antheridium in function, but not at all in 

 structure. The division of this cell follows immediately giving rise to 

 tlie generative and tube cell * * * * 



"No further division takes place until the following spring, a period 

 of about eleven months, and in this condition pollination occurs. * * * * 

 The pollen tube begins to grow into the nucellus as soon as the spore 

 is deposited, and continues to develop until it is checked by cold weather. 

 The next spring (third spring) the tube begins to renew its penetra- 

 tion of the nucellus during April, about a year after the pollen mother 

 cell entered ujDon the reduction divisions, the large tube nucleus enters 

 the tube and at the same time the generative cell divides into the stalk 

 cell and body cell (Fig. 16-L). * * * * After its second start the pollen 

 tube consumes about two months in traversing the nucellus, reaching the 

 archegonium about the first of July." 



An epitome of this data may be presented with the aid of Fig. 16, 

 which is taken from Coulter and Chamberlain.^ 



SUMMARIZATION OF MICROSPORE DEVELOPMENT. 



About May 1-10 — Tetrad Division Mother Spore Cell Fig. 16-A-C 



About May 10-20 — Formation of First Prothallial Cell... Fig. 16-D-G 



About May 20-25 — Second Prothallial Cell cut off Fig. 16-H-J 



About June 15 — Generative and Tube Cell Formed Fig. 16-K 



June 15-May 15 of Second Spring — No Change Fig. 16-K 



About May 15 — Pollination Fig. 16-K 



May 15 — Fall — Penetration of Pollen Tube Fig. 16-L 



About May 1 of Third Spring — Resumption of Growth. . . .Fig. 16-L 

 About July 1 of Third Spring — Fertilizatiori. 



While this data is for P. Laricio it will no doubt stand approximately 

 for the normal condition in P. sylvestris. P'ig. 16-K which represents the 

 condition of the microspore at the time of ijollination is of especial in- 

 terest. In our material (Fig. 17) tliis condition of the microspore 

 showing generative and tube cell was abundantly seen (Fig. 17-3 and 4), 

 indicating a normal develojiment as far as nuclear condition is con- 

 cerned. Tlie anomalous condition of our material is shown by Fig. 17- 



