Jan., 1910,] Monochytrium, a New Genus. 45 



in the usual way, sectioned 0- lO/i thick, and stained on the shde 

 with Heidenhein's Iron Alum Haematoxylon and with Analin 

 vSafranin and Gentian Violet. Either stain is satisfactory but 

 most of the drawings have been made from material stained with 

 the Safranin- Violet combination. 



The youngest stages of the parasite fotmd were imbedded in 

 the cytoplasm of the host cell (Fig. 2). They were minute 

 amoeboid cells whose size (3//) corresponds rather closely with 

 that of the segments of the zoosporangium. Not infrequently 

 the perforations bv which the voung parasite had entered the 

 host cell may be seen in section as thickenings on the inside of 

 the wall of the host (Figs. 8, 10). In rare instances slight thick- 

 enings mav also be observed on the outside surface of the wall 

 (Fig. 13). In other cells cut tangentially so as to allow one to 

 look through the perforations (Fig. 3) one sees that the holes are 

 surrounded bv irregular cellulose thickenings. In appearance 

 these collars resemble somewhat the irregular growths of bark 

 around a healing wound on a tree trunk and suggest that they 

 were secreted b}^ the cytoplasm of the host cell in an attempt to 

 repair the damage; in many instances there are indications that 

 such repair is completed for. in most of the infected cells the 

 points of entrance appear to be simplv thickened places on the 

 walls and no perforation can be observed bv focusing up and 

 down. 



In favorable locations the young amoebulae imbedded in the 

 host cvtoplasm are extremelv abundant, hardly a cell being free 

 from parasites (Fig. 1). Moreover, there are frec^uently nearly a 

 dozen in a single cell (Fig. 2). Their minute size precludes ver\' 

 exact observations as to their structure but as compared with 

 the segments of the zoosporangia from which they are supposed 

 to have come their cvtoplasm is less dense, containing, appar- 

 ently almost from the beginning, several relativelv large vacuoles 

 (Fig. 5), between the meshes of the reticulate cytoplasm. Of 

 the nucleus little can be seen beyond the deeply staining nucleolus 

 and the nuclear membrane, though bv analog}' with the larger 

 nuclei of later stages it may be supposed to have more or less of a 

 chromatin reticulum in addition. Lying in the cytoplasm close 

 beside the nucleus there is frequentlv a deeply staining body 

 (Figs. 5, 6) whose general appearance at once suggests a centro- 

 some. No such structure was observed at any other stage of the 

 life history but it is not impossible that one mav be associated 

 with the flagella of the zoospores. But as long as the zoospores 

 themselves remain unknown it is idle to speculate on the matter. 

 The deeply staining bodies in question occur, however, with suf- 

 ficient frequency to make it very desirable to be able to offer some 

 interpretation of their presence. 



