22 BOTANICAL GAZETTE [jaxc^ry 



o 



the count of chromosomes which was made 

 ^st division, the daughter nucleus may con 



be 



or 66 chromosomes, the reduced number; however, it should 

 remembered that this is certainly due to the obliteration of the longi- 

 tudinal fission which appeared in the anaphase, and since this eafly 

 part of the event of the second mitosis is actually initiated in the ana- 

 phase of the first division, the daughter chromosomes should well be 

 considered as bivalent, consisting of two granddaughter chromosomes, 

 although the actual separation is completed in the prophase of the 

 second division. Therefore the homotvpic di\dsion. in soite of its 



dependence upon the first 



completes the process initi 



mitosis: in 



is initiated m the heterotypic mitosis, but the reduction of the first 

 division is only apparent ; the real reduction in the number of chromo- 

 somes is completed in the telophase of the second division. It follows 

 that the first nucleus which contains the reduced number of chro- 

 mosomes is the spore, and consequently the spore marks the starting- 

 point of the new generation, as discussed by Gregoire (25). 



Centrosome.— The presence of the centrosome among the pterido- 

 phytes was reported in the spore mother cell by HuiiPHREY (29) 

 in Psilotum and Osmunda, and by Calkins (ii) in Adiantum and 

 Pteris. OSTERHOFT (35) denied the presence of the centrosome in 

 the spindle formation of Fquisetum. 



In Nephrodium, the spindle always arises from the rearrangement 



In sporogenesis a multipolar polyarch spindle is first 

 obserj-ed when the nuclear membrane disappears, while in typical 

 mitosis in the vegetative cell, two kinoplasmic caps first appear at 

 the poles of the nucleus before the disappearance of the nuclear mem- 

 brane. In both cases when chromosomes are arranged in the equa- 

 tOTiai plate, spindle fibers gather mto a focal center which lacks the 

 centrosome or centrosphere, and the gathering of the fibers into the 



asm, 



persists until the last an 



how- 



ever, m no stage of mitosis are there present centrosomes, radiations 

 centrc^pheres, or any kind of structure which was beHeved to contro 

 nuclear division. As regards the mechanism of mitosis, the write] 



any 



ome 



