May, 1909.] 
Amitosis by Constriction. 
5 T 4 
A NOTE ON AMITOSIS BY CONSTRICTION IN 
SYNCHYTRIUM.* 
Robert F. Griggs. 
In a former articlef 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 though 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. XLVI. 
t Griggs, R. F. Some Aspects of Amitosis in Synchytrium. Bot. 
Gaz. 47: 127-138, 1909. 
