Feb. 26, 1917 
Internal Telia Produced by Cronartium sp. 
33i 
ning to develop the wall thickening and color change. The walls of the 
spores at the tip of the telial column shown in Plate 88, C, were identical 
in color and thickness with the walls of spores in external columns. 
The measurements of the internal spores, 10 to 20 by 20 to 40 ft, agreed 
well with those of normal spores, considering the conditions under which 
the internal spores were produced. There was at first some doubt as to 
the true nature of the spores, for some of the sori were surmounted with 
a peridium like the peridium of a normal uredinium. This would not 
exclude the possibility that the sorus was a telium, for the normal telial 
column often arises from an old uredinium. In this case, indeed, there 
could be no question whether the spores were urediniospores or telio- 
spores, since the mycelium, which, as mentioned above, sometimes 
stuffed the pith region, was typically binucleate; the spores were uni¬ 
nucleate; and the change from the binucleate condition to the uni¬ 
nucleate condition occurred just after the spores were cut off from the 
basal cells of the sorus. This cytological evidence, agreeing as it does 
with cytological conditions in sori producing teliospores, completely 
established the identity of the internal sori as telia, even when the 
spores were very young. 
The occurrence of the petiole infection is rather common in both wild 
and cultivated species of Ribes where the general infection is heavy. 
In two other species examined, R. nigrum L. and R . cynosbati L., no 
internal telia had been formed, although the mycelium was abundant 
and normal telia present on the surface of the petioles. The epidermal 
region of the petioles of Ribes spp. undoubtedly offers more resistance 
to the developing telia than the epidermis and palisade cells of the leaf. 
The sori probably are unable to break through the stiffer layer in the 
petiole; hence, their development as far as possible within the inclosing 
tissue. Unquestionably internal sori should be regarded as rather 
common teratological phenomena, developed in spite of their unfavor¬ 
able position. Morphologically they have no special significance. Their 
development is to be expected 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. Accidental discov¬ 
ery of the sori after the material had been killed and embedded has pre¬ 
cluded any spore germination experiments. Investigators, however, 
have found the internal mycelium, and the teliospores themselves, to 
be in a living state after a considerable time, even in comparatively dry 
tissue. Pritchard (5) figures the teliospores as undergoing a sort of 
palmella-like division which may be the equivalent of germination. In his 
material the mycelium was certainly alive for a long time. There is a 
possibility that the phenomena described by Pritchard (5) might be 
observed under suitable conditions in the internal teliospores of Cronar¬ 
tium ribicola . 
