Charles J. Chamberlain 15 



phytes, if the centrosome should prove to be present throughout the life-history, it is at 

 least much more conspicuous at some phases than at others. Plants furnish numerous 

 illustrations of the gradual reduction, and even the disappearance of organs during 

 phylogeny Most botanists admit that in the earliest sporophytes all the cells were 

 sporogenous; but, during phylogeny, portions of the sporogenous tissue became steril- 

 ized until the sporogenous tissue finally became much limited in extent and now 

 appears only during a few cell-generations. During such reductions, functions of 

 cells or organs may become completely changed, as in the case of the elaters of 

 liverworts, which are, historically, sporogenous cells and often develop like sporoge- 

 nous cells, even up to the spore mother-cell stage. In the formation of the ascospore, 

 the function of the centrosome is not the same as during the mitotic divisions in the 

 ascus. Other examples might be cited. 



That the function of the blepharoplast is somewhat peculiar must be admitted. 

 Radiations, however, and spindle fibers, which are often the most conspicuous accom- 

 paniments of centrosomes and centrospheres, are actively concerned in movement and 

 are not essentially different from the radiations or cilia of blepharoplasts. In form 

 and function centrosomes present so much diversity among themselves that the peculi- 

 arities of the blepharoplast need occasion no surprise. One has only to compare the 

 typical spherical centrosome with the rod-like centrosome of Dictyota, the hollow 

 cylindrical spindle of some diatoms, and with the centrosome which forms the Haut- 

 schicht of the ascospore. 



We should conclude, therefore, that centrosomes, centrospheres, and blepharoplasts 

 are historically related, and with their radiations, spindle fibers, and cilia are only dif- 

 ferent manifestations of kinoplasmic activity, movement in all cases being the principal 

 function. 



Pellia, with the prominent aster and centrosphere of its germinating spore 

 becoming less and less distinct in succeeding mitoses until a condition is reached 

 resembling that which prevails in the flowering plants, presents in its own life-history 

 a great reduction of the aster and the disappearance of the centrosphere. 



I am deeply indebted to Professor Strasburger for his kindly courtesy and help- 

 ful suggestions during my work in his laboratory. 



SUMMARY 



1. The principal part of the work deals with the first three divisions in the ger- 

 minating spore of Pellia epiphylla. We have not intended to attack the excellent 

 work of previous investigators, but rather have attempted to extend a little farther a 

 knowledge of the phenomena of -mitosis. 



2. A centrosphere, but no centrosome, is very prominent during early prophases 

 of the first mitosis in the germinating spore. The centrosphere is not present at all 

 during the subsequent stages of mitosis. An aster is also conspicuous during the 

 early prophases* of the first mitosis, but disappears before the metaphase is reached. 



341 



