RicE: INTERNAL SORI OF PUCCINIA SORGHI 47 
rather unusual infection induced in the succulent parenchyma 
of stem and ear the host conditions have seemed to stimulate 
the parasite to both vegetative and reproductive excesses, as 
evidenced by the abundant mycelium emeshing the internal 
sori. Although Hungerford (11) does not make the point, it 
seems to me his description of internal teleutosori in the wheat 
seed involves also good evidence of excessive reproductive 
activity. He believes these sori in the wheat seed have ‘‘no 
special significance but the infection spreads to these tissues 
(from the rachis or rachilla) just as it does from an infection 
point in any of the vegetative parts of the plant.”’ 
A third point of agreement is that hea interiat soriin the corn 
all occurred when the parasite by the abund- 
ant intercellular mycelium and the heavy external spore forma- 
tion. So far as I can judge this was true in the cases described 
by others. 
Fourth, in the cases described in the corn the sori occur, 
with one exception, in thin-walled parenchyma tissue: along the 
midrib of the leaf, in mesophyll between the bundles, in the 
deeper stem parenchyma, in soft tissue of the ear. The freedom 
of development which such tissue allows to the fungus is striking. 
In more resistant tissue this very freedom of development re- 
solves, it seems to me, into development along the line of least 
resistance. This is the explanation which Colley (8) offers for 
reversed polarity in some aecidial sori of Cronartium ribicola 
where he states the aecidial chains grow toward the center of 
the tree, usually into a resin-duct. Dodge (8a) describes deep- 
seated uredosori of Pucciniastrum americanum in the stem of 
Rubus strigosus. Some lie deep in the cortex with the peridium 
on the inner side, just outside the cork cambium and Dodge 
suggests that such inversion may ‘‘facilitate spore discharge 
the following spring as the cortical parenchyma peels off.” 
Other sori which lie only two or three cells deep beneath the 
epidermis are erect. In both these cases there is apparently 
development along the line of least resistance. It seems well 
illustrated also by Clinton’s (5) case of aecidia of Gymnospcrang- 
ium in the seed cavities of the apple fruit and by Miss Stamfli’s 
(21) figure of spermagonia of Uromyces Pisi at the insertion of 
abortive seeds in Euphorbia capsules. Thus the same cause may 
underlie the development of internal sori in widely differing 
