150 BOTANICAL GAZETTE [march 



the following solution: i per cent, chromic acid 25 cc , i per cent, 

 glacial acetic acid i5 cc , i per cent, osmic acid io cc , water 5o cc . The 

 methods used after the material was thoroughly washed were similar 

 to those given in the previous paper on sporogenesis (101). 



Description 



VEGETATIVE MITOSIS IN PROTHALLIA 



Immediately after the germination of the spore, the nucleus in the 

 prothallial cell is quite large, but shows a tendency to diminish gradu- 

 ally during the further development of the prothallia into many-celled 

 stages. The events of the mitosis in any vegetative cell of a prothal- 

 lium are not only repetitions of the same type, but they are similar to 

 those of the sporophyte. For this reason no detailed account will be 

 made at this time, but a few essential points deserve mention. 



The chromatin reticulum of the resting nucleus of the prothallia, 

 which has a ragged structure like that in a vegetative cell of the sporo- 

 phyte, becomes transformed into a spirem that runs an irregular course 

 within the nucleus, many tangled parts or loops coming into close 

 contact with the membrane. The spirem then becomes rather smooth 

 and uniform in thickness and very likely there is present a con- 

 tinuous spirem (fig. i). A kinoplasmic cap of conical shape appears 

 at each pole of the nucleus, consisting of a few fibers arranged along 

 the lateral edges of the cone. With the dissolution of the nuclear 

 membrane at the two poles, the fibers push in and attach themselves 

 to the chromosomes which have just segmented from the spirem 



(fig- *)• 



The points at which segmentation of the spirem into chromosomes 

 may occur have a certain regularity in relation to location within the 

 nucleus. Although it is impossible to give an accurate explanation 

 of the mechanism at present, the fact that many free ends of the 

 chromosomes, immediately after segmentation, are directed toward 

 the poles may prove that the segmentation took place in bent points 

 of loops. Longitudinal splitting of the chromosomes appeared after 

 the completion of this segmentation. 



Contemporary with the entire dissolution of the nuclear membrane, 

 the chromosomes show a tendency to arrange themselves parallel to 

 an axis passing between the two poles (fig. j). The daughter halves 



