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 

 Raeweed, Ambrosia artemisifolia, infested with Rhodochvtrium 

 spilanthis the cvtology of which had interested the writer in 

 connection with his work on vSynchytrium, 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 Rhodochytrium except its ho'st plant, being dis- 

 tinct in all of the details of its cytology as well as in its method of 

 parasitism and its life history. AVhereas Rhodochytrium 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 rarelv the chlorenchvma 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 Rhodochytrium 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, how^ever, fruitless, which, is not surprising in view of the 

 habits of the fungus. For while the parasite is extraordinarih' 

 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 thev were abundant. The Rhodochytrium material from 

 which the slides were made was supplied me by the kindness of 

 mv 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 E)r. Stevens to Professor 

 Atkinson from which he published his two notes on Rhodochy- 

 trium. It was killed in Chromacetic acid, imbedded in paraffine 



* Contributions from the Botanical Laboratory' of the Ohio State 

 University No. 51. 



