Division of the Generative N tic tens in Pines . 217 
inequality in the size of these nuclei is very early apparent, 
and becomes more pronounced as they reach maturity. 
10. The sperm-nuclei soon come to lie together in the 
upper part of their cytoplasm and early attain their full size, 
the larger one being invariably in advance. 
The nuclear reticulum, at first delicate, soon becomes very 
dense, but there is no evidence of the presence in these nuclei 
of a special metaplasmic substance. 
11. At the time when the sperm-nuclei come into contact 
or nearly so, the pollen-tube has penetrated little, if at all, 
beyond the nucellar tissue of the first year’s growth. Now, 
however, it again begins to elongate, and its downward course 
through the new nucellar tissue is extremely rapid. 
12. When just above the egg, the apex of the pollen-tube 
is filled with cytoplasm. The vegetative nucleus lies in the 
upper part of this cytoplasm, and near it is seen the stalk-cell 
still in contact with the lower- portion of the cytoplasm which 
surrounds the sperm-nuclei. 
13. No individualized centrosome has been observed ; but 
the existence of the diffused centrosome is suggested in 
connexion with the division of the generative nucleus. 
14. The above summary holds good, when not otherwise 
indicated, for all five species of pines which I have studied. 
Nuclear phenomena are found to vary so much, even within 
the limits of a given genus, that it no longer seems safe to 
consider the details of development in a single plant as typical 
of a large group of plants. We therefore make no general- 
izations regarding the Abietineae. And we hesitate even to 
draw conclusions for the genus Pinus , for while the agreement 
in certain phases of development of five species would seem 
to be sufficient for the formulation of a rule, there may still 
exist within the genus individuals which are, in certain aspects 
of nuclear activity, a law unto themselves. 
