44 
The Ohio Naturalist. 
[Vol. X, No. 3, 
MONOCHYTRIUM, A NEW GENUS OF THE CHYTRIDIALES, 
ITS LIFE HISTORY AND CYTOLOGY.* 
Robert F. Griggs. 
In working over sections of leaves and stems of the common 
Ragweed, Ambrosia artemisifolia, infested with Rhodochvtrium 
spilanthis the cytology of which had interested the writer in 
connection with his work on Synchytrium, he found that there 
was present along with the Rhodochvtrium another parasite. It 
was at first supposed that the new plant was an early stage of 
Rhodochvtrium but it was soon found that it had nothing in 
common with Rhodochvtrium except its host plant, being dis- 
tinct in all of the details of its cytology as well as in its method of 
parasitism and its life history. Whereas Rhodochvtrium is an 
intercellular parasite infesting the fibrovascular bundles of its 
host into which it sends numerous haustoria to gather its nutri- 
tion, the new plant which I shall term Monochytrium leads an 
intracellular existence within the epidermal, hypodermal or 
more rarely the chlorenchyma cells of its host thus resembling in 
its mode of life such species of Synchytrium as S. taraxici, a 
resemblance which is further increased by the absence of haus- 
toria. From these plants, however, Monochytrium differs mark- 
edly in the binucleate sexual resting spores and in the solitary 
zoosporangia in allusion to which the generic name has been 
chosen. 
After Monochytrium was discovered a considerable amount 
of the Ragweed infested with Rhodochvtrium was examined in 
the hope of detecting the new parasite in the living state and of 
observing its grosser characters and its zoospores. This search 
was, however, fruitless, which is not surprising in view of the 
habits of the fungus. For while the parasite is extraordinarilv 
abundant in certain small areas of the sections (Fig. 1), such 
areas are seldom found. Out of 200 slides Monochytrium was 
observed in only 10. Furthermore, the parasite deforms its host 
only very slightly so that infested areas would not be easy to find 
unless they were abundant. The Rhodochytrium material from 
which the slides were made was supplied me by the kindness of 
my good friend, Professor F. L. Stevens, and his colleague, Mr. 
J. G. Hall of the North Carolina Agricultural Experiment Sta- 
tion. It was collected at Raleigh on July 3, 11, and 18, 1908, 
and was a portion of the material sent by Dr. Stevens to Professor 
Atkinson from which he published his two notes on Rhodochy- 
trium. It was killed in Chroinacetic acid, imbedded in paraffine 
* Contributions from the Botanical Laboratory of the Ohio State 
L T niversity No. 51. 
