May, 1909.] Amitosis by Constridmi. 513 



A NOTE ON AMITOSIS BY CONSTRICTION IN 

 SYNCHYTRIUM.* 



Robert F. Griggs. 



In a former article f dealing with amitosis in the parasitic 

 fungus, Synchytrium, the writer mentioned beside the peculiar 

 processes of direct nuclear division which he termed Nuclear 

 Gemmation and Heteroschizis, a third sort of amitosis which 

 resembles closely the more commonly reported process of ami- 

 tosis where the nucleus elongates and divides by constriction or 

 by the formation of a septum across it. Because he had observed 

 only a relatively small number of such cases at the time of 

 writing the former paper he contented himself with mere mention 

 of the process. Since that time, however, a considerable number 

 of such constricting nuclei scattered through a score of cysts 

 have been found. From an examination of these cases the 

 writer has been fully convinced that this is a normal process 

 which is to be ranked along with the other methods of amitosis 

 in multiplying the nuclei of the parasite preparatory to zoospore 

 formation. 



The mechanism by which amitosis is accomplished by con- 

 striction is as simple as could well be. Different parts of the 

 chromatin of the nucleus separate and move apart, forming two 

 or more lobes ; these round off and each becomes an independent 

 daughter nucleus. This process usually occurs in spirem, but in 

 rare instances neither the daughter nuclei nor the remaining 

 undivided nuclei in the cyst are in that condition. Amitosis by 

 constriction occurs for the most part in early stages when nuclear 

 gemmation is only just beginning and long before heterochizis 

 is observed. Even the primary nuclei may divide in this man- 

 ner thotigh in the species studied, S. decipiens, they nearly 

 always divide mitotically. Occurring thus early in the cycle of 

 nuclear multiplication this process is usually but an incident in 

 the history of the chromatin thus divided, for after a very brief 

 existence the daughter nuclei are further subdivided by other 

 sorts of amitosis (Figs. 3-4). 



It is manifestly impossible to follow the history of the nuclei 

 thus derived by constriction (or their chromatin content) further 

 than their division which is usually accomplished by nuclear 

 gemmation. But evidence was presented in the previous paper 

 which shows that the small nuclei derived by that process are 

 normal and become the ancestors of the zoospores which form 



* Contribution from the Botanical Laboratory of the Ohio State Uni- 

 versity, No. XL VI. 



t Griggs, R. F. Some Aspects of Amitosis in Svnchytrium. Bot. 

 Gaz. 47: 127-138, 1909. 



