36 CEANBERRY DISEASES. 



THE FUNGUS (eXOBASIDIUM OXYCOCCI, ROSTR.) CAUSING HYPERTROPHY. 



In this, like all Exobasidii, the mycelium of the fungus infests 

 the tissue of the leaves and stems, producing the hypertrophied con- 

 dition described above. The basidia are elongate clavate, and are 

 produced at the extremities of the hyphse. They emerge on the 

 surface of the aifected part of the host and produce usually four 

 basidiospores at the ends of short, slender sterigmata. The spores 

 are usually somewhat fusiform, slightly curved, and hyaline, measur- 

 ing 1-t by 3.5 fx. They proceed to grow soon after falling and may 

 be seen in old specimens in different stages of germination. From 

 one to three transverse septa are usually formed, after which a germ 

 tube arises from either or both ends, which produces conidia somewhat 

 resembling the basidiospores, but smaller. The fungus, when mature, 

 gives a fine, gray, powdery appearance to the surface of the distorted 

 parts of the host. 



Relationshij) to other Exohasidii. — This species, so far as it has 

 been studied, agrees in morphological characters with Exohasidium 

 vaccina (Fckl.) Wor. The spores of Exohasidium vaccinii are, 

 according to Saccardo, 5 to 8 by 1 to 2 /a. This, according to 

 Woronin,'-' Richards,^'' and others, is an error, as the basidio- 

 spores usually range from 14 to 17 by 3 /x. The error possibly arose 

 from the confusion of basidiospores with conidia, which are fre- 

 quently present, especially in specimens which are getting old. 



The typical form of Exohasidium vaccinii occurs on Vacehmwi 

 vitis-idaea, producing hypertroj^hied spots on the leaves. No record 

 has been found of the occurrence of hypertrophied shoots on this 

 host similar to those found on cranberry plants. Rostrup ^^ seems 

 to have been the first to describe this form. In 1883 he re^jorted it 

 as occurring on Oxycoccus palustris in Denmark. His description 

 accords exactly with the specimens w^e have found on the cranberry 

 plant. He says he could not find the two forms, i. e., the one pro- 

 ducing spots on the leaves, typical Exohasidium vaccinii^ and the one 

 producing hypertrophied shoots, Exohasidium oxycocci, on the same 

 plant, but the two were found in the same locality in one instance. 



An Exohasidium also occurs on cranberry plants in Massachu- 

 setts, which produces spots on the leaves like those produced on 

 Vacciiiium vitis-idaea, and agrees also in all microscoi^ical characters 

 with Exohasidium^ vaccinii (Fckl.) Wor. (PL VII, A and B). No 

 specimens of the two forms could be found on the same plant or 

 in the same vicinity. No cross-infection experiments with these two 

 forms have been tried on these hosts so far as known, and as the 

 observations already made seem to indicate the ^jrobability of their 



110 



