CHROMOSOMAL VESICLES IN PHASEOLUS. 2K) 



the present time which would justify the conclusion that in any 

 other plants or animals the prophase chromosomes are formed 

 in the same way as in the bean. 



Martins Mano states that the nucleolus of Phaseolus does not 

 contribute to the formation of chromosomes. The figures of the 

 present paper as well as those of Wager are quite conclusive on 

 this point and show that he was mistaken. 



The Nucleolus or Karyosome. In the many descriptions and 

 discussions of chromatin nucleoli the various authors have not 

 taken account of the fact that the nucleolus may be made up of 

 a non-alveolized portion of every chromosome, as in the case in 

 Phaseolus. If the chromatin nucleolus is a store-house for chro- 

 matin it is quite natural that it should be found at the meeting 

 point of all the chromosomes, since the latter remain distinct 

 throughout the resting phase of the nucleus. 



Continuity of Chromosomes. The significance of chromosomal 

 continuity for various problems of cytology and genetics has been 

 completely discussed previously, even before Richards had, for 

 the first time, traced chromosomal vesicles through the inter- 

 kinetic nucleus (Moenkhaus, 1904; Conklin, 1902; Wenrich, 

 1916; Richards, 1917; Wilson, 1925). A repetition of this 

 discussion would be superfluous. 



SUMMARY. 



1. When the chromosomes of Phaseolus reach the poles of the 

 spindle they come in contact with each other, all lying parallel 

 to the long axis of the spindle. The individual chromosomes can 

 be traced by the indentations on the surface of the chromatin 

 mass. 



2. Vacuolization of chromosomes begins in the end nearest the 

 equator of the cell (the proximal end). 



3. The distal ends of the chromosomes do not become alveo- 

 lized, but join to form the chromatin nucleolus. There is no 

 plasmasome present in the root-tip cells of Phaseolus. 



4. The linin sheath of the chromosomes becomes visible in 

 conjunction with the telophasic vacuolization and can be traced 

 through the interphase and resting condition, thus showing that 

 the chromosomes remain distinct from one mitosis to the next. 



