184 Darling: Sex in dioecious plants 



exception Is that of Spirogyra \ but because of the very small size 

 of the chromosomes there has arisen among the workers on this 

 genus a difference in interpretation of the observations which leaves 

 the case at present in a very uncertain position. 



It is important to note that all of the work done on the forma- 

 tion of the chromosomes in the plant cells has been done on 

 hermaphrodite forms. 



Observations on the pollen spore formation in Acer 



Negtindo 



It was my purpose in taking up this study to determine if there 

 is a behavior of the chromosomes in dioecious plants analogous 

 to that found in the spermatogenesis of insects, and apparently 

 having to do with the determination of sex* After examining the 

 anthers of several of the dioecious Angiospermae, I found in Acer 



m 



Negtindo L., a maple reported to be strictly dioecious, a nucleus 

 with comparatively few chromosomes. Another feature which 

 makes this plant especially favorable for study, is the successive 

 stages of development found in each loculus of the anther, the 

 youngest stages being at the base, the oldest at the top. 



The mother cells in the early stages are differentiated from the 

 surrounding tapetal cells in possessing a greater amount of chro- 

 matin-staining material in the form of a single, spherical nucleolus. 

 A small amount of linin is visible with a few nodes or denser por- 

 tions, but these do not take chromatin stain (fig. l). ^ 



The first visible change of the cell during the early growth 

 period, is a slight increase in size of the nucleus and the appear- 

 ance of a small bud-like process on the nucleolus (fig. 2). This 

 chromatin-staining mass gradually comes from the nucleolus in the 

 form of a spherical body ; at first it seems to be attached by a 

 thread but soon becomes free and migrates to the nuclear wall, 

 where it becomes connected with the linin and soon diffuses out 

 upon it to build up the spireme thread (figs. 3-6). Soon after the 

 first body is given off another one appears and behaves in the same 

 manner as the first (figs. 5, 6). From the fact that these bodies 

 gradually lose their chromatin-staining capacity and the reticulum 

 at the same time becomes more apparent, there can be little doubt 

 but that these are masses of chromatin which go to make up the 

 spireme thread. 



