40 Rice: INTERNAL SORI OF PUCCINIA SORGHI 
mycelium.’’ Colley (7) thinks internal sori are to be expected, 
in spite of unfavorable position, whenever the point at which 
the sorus begins to form is located beneath a layer of tissue 
which offers a greater resistance than the developing sorus can 
overcome. In the many cases where internal sori are obviously 
formed under conditions which afford ample space it may still 
be that the line of least resistance isinward. The point of interest 
in both these cases is why the fungus should form spores under 
either of these conditions. Miss Marryat (12a) reports a very 
interesting case in the formation of abortive sori in immune 
Einkorn wheat. They lay beneath the epidermis and deep down 
in the leaf tissue. The spores however were small, ill-shaped, 
Fic. 1. Uredospores in a pocket at the base of an external sorus on a 
corn leaf. Stalks of the uredospores are represented diagrammatically and 
incomplete as they were shrunken in the preparation. Drawing made with 
camera lucida, X 160. 
and scarcely recognizable as such. This would seem to be a 
case in which the general impoverished condition of the fungus 
had led to widespread abortive attempts at spore formation in 
the mycelium. 
I found internal sori of Puccinia Sorghi on corn grown in the 
plant house of Columbia University during 1921 and 1922. 
The material was fixed in Fleming ’s medium solution, cut 7.5 u 
thick, and stained with triple stain. Two instances of uredosori 
were observed: one in a leaf, the other in a leaf sheath. Several 
instances of teleutosori were found: in the leaf, in the leaf sheath, 
in the stem, and in the soft tissue of an abnormally branched ear. 
The first instance was one of uredospores found in April 
1921, in sections made through an erumpent sorus upon a mature 
