14 Mitosis in Pellia 



of the nucleus and cell, but Karsten was not able to identify the body positively until 

 the radiations began to appear. Davis (5) describes a centrosphere, but no centro- 

 some, in the tetraspore mother-cell of Corallina. The centrospheres give rise to the 

 spindle, and consequently play an essential part during nuclear and cell division. No 

 centrospheres could be recognized during the resting-stage of the nucleus. 



Thus it appears that in many of the algse well-defined centrosomes are present, at 

 least during certain phases of the life-history, and that the centrosomes may divide 

 and persist from one cell-generation to another, while in other algse the centrosome 

 does not show such a degree of permanence. In the algsB which we have mentioned 

 the centrosomes are not surrounded by a clear area. In Corallina it is to be noted 

 that there is no centrosome, but only a centrosphere. In none of the algse have centro- 

 somes been traced throughout the life-history of the plant. In some fungi centro- 

 somes are present during the mitoses concerned in the development of spores. Among 

 the liverworts we doubt whether there is, at any period in the life-history, a centro- 

 some like those described for the Thallophytes. The centrosphere appearing and 

 functioning during only a few mitoses, has replaced the functional centrosome. 



The polar radiations which are often conspicuous during mitosis in Pteridophytes, 

 Gymnosperms, and Angiosperms, are of the same nature as those of Thallophytes and 

 bryophytes, but in the higher groups (and, possibly, in most mitoses in the lower 

 groups) a definite centrosome, or even a centrosphere is lacking. Centrosomes and 

 centrospheres in vascular plants have been described and figured so frequently by such 

 competent observers that he would be rash, indeed, who would claim that all such 

 accounts have no foundation except in perverted imagination and preconceived theories. 

 That theories suggested by the accounts of zoologists and supported principally by 

 misinterpretations of plant structures have caused exaggeration in the drawings and 

 descriptions of botanists is probably true. While we believe that most of these 

 centrosomes are to be interpreted as chance granules, nucleoli, pieces of chromosomes, 

 etc., still we see no reason why a centrosome or centrosphere might not occur occa- 

 sionally through atavism. The finely granular areas which have been noted during 

 spermatogenesis in Coniferales and the similar areas which are often seen in Angio- 

 sperms, are, in our opinion, vestiges representing historically the centrosphere as it 

 appears during the early mitoses in the germinating spore of Pellia. 



The blepharoplasts described for various Pteridophytes and Gymnosperms 

 are, in our opinion, to be interpreted as centrosomes. It seems to be true that in 

 Ginkgo (17), Cycas (19), and Zamia (39) they appear only in the body cell and in the 

 spermatozoids. In Marsilea, however, Shaw (29) traced them another cell-generation 

 farther back, and in the same genus Belaje£P (2) found blepharoplasts even during the 

 earlier stages in the development of spermatogenous tissue. But, granting that the 

 blepharoplast appears during only one or two cell-generations, this does not seem to be 

 a valid argument against its centrosome character, for in Pellia the centrosphere is 

 clearly distinguishable during only a few mitoses, and even in the multicellular Thallo- 



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