Charles J. Chamberlain 11 



erable substance to the growing chromosomes. As the chromosomes increase in size, 

 the nucleoli become more and more vacuolated, and material which resembles that of 

 the nucleoli is often found adhering to the growing chromosomes. After the chro- 

 mosomes have reached their full size, the nucleoli fragment, the fragments usually 

 staining with gentian violet. Soon the entire nuclear cavity becomes filled with gran- 

 ular matter staining with gentian violet, and at this period the central portions of the 

 spindle appear suddenly as the granular matter disappears. A few early spindles 

 were noted in which this central portion did not seem to consist of sharply defined 

 fibers. While such an appearance is often due to faulty methods, the sharply defined 

 fibers in other figures in the same preparation favor the inference that these undif- 

 ferentiated portions represent stages in the transformation of nucleolar matter into 

 spindle fibers. In our opinion, these phenomena support Strasburger's (33) theory 

 that the nucleolus contributes some of the material for the spindle. 



Observations on the chromatin were merely incidental, but it is certainly safe to 

 say that Pellia, in spite of the small size of its nuclei, is a favorable object for such 

 study. As has just been mentioned, the nucleolus probably contributes something to 

 the substance of the chromosomes. Although the chromosomes are small, they can be 

 distinguished very early and seem to lose their identity much later than is usually 

 the case. Mitoses in the venter of the archegonium show a longitudinal splitting of 

 the chromosomes before the breaking down of the nuclear membrane, while in the ger- 

 minating spores the splitting occurs much later. 



The number of chromosomes in the gametophyte, as counted in the germinating 

 spores and in the actively dividing region of the thallus, is eight. This number, how- 

 ever, is far from being constant. Both Farmer (10) and Davis (7) report occasional 

 irregularities. In the present study, a few nuclei were found with only seven chromo- 

 somes, and nine chromosomes were counted in more than a dozen cases (Plate XXVI, 

 Fig. 20). Long spindles upon which the chromosomes are irregularly arranged are 

 not infrequent, and it seems probable that such a mitosis might result in an unequal 

 distribution of the chromosomes, and thus account for variations from the typical 

 number (Plate XXV, Fig. 8). 



THE THIRD MITOSIS IN THE GERMINATING SPORE 



While considerable attention was given to the third mitosis, an extended descrip- 

 tion is hardly necessary. Prominent asters (Plate XXVI, Fig, 19) like those of the 

 two preceding mitoses are often present, but they are frequently absent, and the caps 

 appear with only a few radiations (Fig. 18) or even none at all. There are no radia- 

 tions in the metaphase (Plate XXV, Fig. 7). In short, it is possible to select from 

 the third mitosis a series of stages identical with a typical series from the apical region 

 of the thallus. At the fourth and succeeding mitoses the resemblance to the usual 

 vegetative divisions becomes more and more pronounced, while asters and centrospheres 

 become correspondingly rare. 



337 



