LIFE HISTORY OF PINUS 133 



nutritive spheres. (2) The sexual nuclei do not fuse, and no 

 structure which could properly be called a segmentation-nucleus 

 is ever formed. (3) An achromatic nuclear reticulum becomes 

 very prominent in the sexual nuclei during the prophase of 

 division. (4) The chromatin of the sexual nuclei forms two 

 definite groups which remain distinct until metakinesis. (5) 

 Two chromatic groups, doubtless representing respectively the 

 paternal and the maternal chromatin, appear in the second 

 division following fecundation ; and the indications are that 

 they will again occur in the third division, and perhaps are 

 characteristic of all the mitoses which take place within the 

 oosphere. (6) The nuclei, which enter the egg but play no 

 part in fertilization, show a tendency to divide mitotically. 



The conclusions reached throughout this paper hold 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 is no longer safe 

 to consider the details of development in a single plant as typical 

 of a large group of plants. We therefore make no generaliza- 

 tions regarding the Abietinece. 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 differ, in certain aspects of 

 their nuclear activity, from that which has been found to occur 

 in Pinus Strobus, P. austriaca, P. rigida, P. resmosa and P. 

 montana var. uncmata. 



APPENDIX. 



SOME ABNORMAL CONDITIONS. 



Supernumerary Nuclei in the Male Gametophyte. Cham- 

 berlain ('97) described a multiplication of the normal number of 

 cells in the pollen-grain of Lilium; Arnoldi ('oo) finding more 

 than the usual number of nuclei in the pollen-tube of Cephalo- 

 taxus, considered that more than one tube-nucleus had been 

 formed ; and Coker ('02) has very recently found that both the 

 first and second prothallial cells in Podocarpus may divide 



