48 Rice: INTERNAL SORI OF PUCCINIA SORGHI 
environments. The tendency of the mycelium to get to an open 
surface for fruiting may in one case cause inversion of sori and 
in another, as in the nests which I have figured, cause a con- 
centric radially oriented structure where the open surface is the 
center of the cell. 
The notable point of agreement in these occurrences of inter- 
nal sori in the corn is that the sori all lie under external sori. 
In such connection, it seems to me we must view the internal 
sori as merely the expression of an excess of reproductive activity 
arising under favorable conditions of nutrition and maturity of 
the fungus. The first example described where the internal 
uredo pocket is really enclosed in the stroma just beneath an 
external sorus is good evidence of such an expression even under 
unfavorable circumstances. Here the hyphae forming the 
fruit cluster have developed uredospores not merely on the upper 
side but in their crowded meshes below. The second instance of 
internal uredospores described above is also striking as an expres- 
sion of excess reproductive activity in cramped conditions. 
Here both sides of the leaf sheath had external sori. The older 
were on the inner surface where inoculation occurred. The 
internal sorus is in a central mesophyll cell and from the enclosing 
hyphal strands eurinenh: with two young sori on the outer surface 
as though tl tthrough the 
leaf had frnited; from a tendency toward reproduction, indis- 
criminately within, as well as on the outer surface. The cases 
described by Reynolds (17) of internal teleutospore sori in the 
heavily infected Xanthium leaf, and by Colley (7) in the petioles 
of dead Ribes leaves seem similar instances of reproductive 
excess under crowded conditions. Colley’s (8) description of 
internal uredospores in the stems of Ribes hirtellum indicate 
almost conditions of proliferation. Although at first sight such 
cramped conditions seem to give the most striking evidence of 
excess reproductive activity, the many instances of internal sori 
developed in soft tissues and along lines of least resistance should, 
I think, be similarly interpreted. I see excess reproductive 
activity, for example, in the abundant growth of mycelium 
and formation of teleutosori found in the young succulent ear 
of corn, and again in the parenchyma of a corn stem. The 
internal sori of Uromyces in the carnation leaf (Adams, 1) and 
Cronartium ribicola in the pine stem (Colley, 8) although under 
