Feb. 26, 1917 Internal Telia Produced by Cronartium sp. 331 



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 n, agreed 

 well with those of normal spores, considering the conditions under w^hich 

 the internal spores w r ere 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- 

 Hum ribicola. 



