274 TRANSACTIONS OF THE CANADIAN INSTITUTE. [VOL. V. 



host-plant. Figure 21 represents a broken root-hair, the basal wall of 

 which has become cutinized and consequently forms a sheath where the 

 hypha is passing through. The penetration of the next cell-wall inwards 

 is unaccompanied by this phenomenon. In figure 18 can be seen part 

 of a root-hair, c, on the lateral walls of which are two sheaths, and the 

 hair in this case being intact, sheaths are not formed in the uncutinized 

 basal wall. In the same figure sheaths can be seen at b and d, where the 

 fungus has passed in through ordinary superficial cells of the prothallus. 

 This is apparently of rare occurrence. 



After penetrating about two or three layers of cells, r, the symbiotic 

 filaments, which are from two to four micra in diameter, begin to grow 

 luxuriantly, and fill the succeeding strata of cells, x, with a much-coiled 

 mycelium. If this be examined with a good apochromatic objective, it 

 is possible to discover that it is by no means always filamentous, but 

 that in many cases, the hyphen expand into large thin-walled vesicles, 

 which are often so abundant that they fill the cells with a botryose mass 

 resembling a Completona, figure 19, b and c. In other cells the filaments 

 prevail, ibid. a. It is not difficult to satisfy oneself that the hyphce and 

 vesicles belong to one and the same inyceliuni, figure 19, b. Frequently 

 some of the vesicular structures become ruptured and shrivel up, ibid. 

 Figure 20 shows a freshly infected cell of the prothallus, highly magni- 

 fied, in which the vesicular structures have just begun to form. Often 

 the advance of the symbiont through the prothallus is marked by the 

 penetration of filaments or by a mixed growth oi Iiyphce a.nd vesicles into 

 new cells. Another kind of organ is also found in the mycelium, viz., 

 conidia. These are thick-walled and from fifteen to twenty micra in 

 diameter. They are generally formed at the end, but sometimes, though 

 rarely, in the course, of a hypha, and are filled with a dense, coarsely 

 granular protoplasm. The contents of the conidiuiii are not separated 

 from the filament by a septum and thus resemble the conidia of the sub- 

 form Aphragmium^^ of the genus Pythium. The conidium germinates in 

 situ, forming a tube which often makes its way into the adjoining cells of 

 the host-plant. I have never been able to detect the formation of 

 zoospores from these conidia, and indeed it is difficult to imagine how 

 they could serve as a means of distribution for so completely endopara- 

 sitic a fungus. The stages of formation and germination of the conidia 

 are shown in figure 22, a, b and c. 



It will be seen from the above account that the symbiont of j9(7/r;/^,^zz/;« 

 virginianum presents several rather remarkable characteristics. In its 

 mode of penetration it resembles Completoria complens, as described by 



II. Rhabenhorst, Krypt, Flora. Fischer, Phyconiyceten, p. 397. 



