46 Rice: INTERNAL SORI OF PUCCINIA SORGHI 
sori Bolley ascribes to a fusion of host cells and fungal hyphae 
which imprisons the spores before they have become strong 
enough to rupture and throw off the epidermis. He makes the 
following suggestion that the subepidermal sori exemplify a 
further specialization in the interrelation of host and parasite. 
It is in completion of the sorus under the uninjured epidermis that the 
fungus displays a high degree of parasitism in that, when mature, the mat of 
fungal tissue which surrounds the spores becomes essentially a part of the 
host 
- the corn, on the contrary, single host cells come to enclose 
the abnormally placed sori. 
In the several cases of internal spores described for the corn 
rust there are certain points of agreement which need to be con- 
sidered in any discussion of the significance of the phenomena. 
First, the cases all developed in the latter part of the winter or in 
the spring: a period in which the greenhouse begins to afford 
better growing conditions for corn. It is a matter of repeated 
observation with greenhouse cultures that from fall through the 
early winter it is difficult to grow corn and hard to maintain 
rust cultures on it. 
Again it has happened so far that the internal sori all occurred 
in mature, although still more or less succulent tissue, on plants 
where many leaves were yellowing, but it is doubtful whether 
in the case of the corn, ageing of the tissue has anything to do 
with the production of internal sori. Other authors reporting 
internal sori have given no evidence upon this. point. I am 
inclined to think that in general in corn as in many hosts of 
rusts the conditions of teleutospore formation support Morgen- 
thaler’s (13) conclusion from experiments with Uromyces Veratrt 
upon Veratrum album that the nutritive supply of the host is an 
all important factor, and that greater age in the host is one of 
the conditions which by disturbing the nutritional functions 
checks uredo, and stimulates teleuto formation. But in the mat- 
ter of the production of internal sori in the corn the occurrence 
of internal as contrasted with external teleutosori seems merely 
an example of excessive reproductive activity. In the first case 
which I described in the corn the long confluent external sorus 
on the leaf repeats itself in a succession of cysts just within in the 
soft parenchyma. The second instance shows internal sori in a 
leaf already heavily encrusted on both surfaces by sori. In the 
