124 MARGARET C. FERGUSON 



chromatin from a finel}'^ divided network is certainly strongly in 

 favor of the theory of the individuality of the chromosomes ; and 

 it is this phenomenon, noted many months before microsporo- 

 genesis was carefully studied, together with the method of the 

 origin of the chromosomes in the first and second divisions of the 

 microspore-mother-cell, that inclines me to accept the view that 

 the chromosomes in the homotypical division of the microspore- 

 mother-cell are identical with those formed in the metaphase of 

 the heterot3^pical mitosis.^ Moreover, this phenomenon, here 

 observed for the first time in plants, would seem to add substan- 

 tial interest from a cytological point of view to Mendel's laws 

 which are at present being so ardently discussed both by animal- 

 and by plant-breeders. 



Riickert ('95) found that the chromatic portions of the conju- 

 gating nuclei in Cyclops not only remain distinct during the 

 first division, but the two groups of chromosomes, representing 

 respectively the maternal and the paternal chromatic elements, 

 could still be recognized after several divisions had taken place. 

 In this case, however, the two groups do not fuse in the daughter- 

 nuclei but a double nucleus is formed in the resting stage. In 

 the same year Zoja ('95) observed that in Ascaris the maternal and 

 the paternal chromosomes remain entirely distinct during several 

 successive divisions of the segmentation nucleus. We have, 

 then, in this second division a further point in which fertiliza- 

 tion-phenomena in Piiius correspond to those which occur within 

 the ova of some animals. I have, as yet, made no attempt to 

 obtain a complete series of stages in the development subsequent 

 to the formation of the first four nuclei of the proembryo. But, 

 from a comparison of fig. 252, <5, plate XXIII, with 244, plate 

 XXII, and 253, /;, plate XXIII, with 237, plate XXI, one is led 

 to expect that the third division following fertilization will corre- 

 spond in all points with the second. It would be interesting to 

 determine if two chromatic groups are characteristic of all 

 divisions which normally occur within the oosphere of Pinus^ 

 and I hope to investigate this question more thoroughl}'' at some 

 future time. 



The Four Segmentation Nuclei. — As a rule, these nuclei 



' See note at close of Appendix. 



