NEGATIVE HELIOTROPISM OF UREDINIOSPORE GERM- 
TUBESi 
F. D. Fromme 
During the course of some germination tests with urediniospores 
of Puccinia Rhamni (Pers.) Wettst. in the spring of 1913 an apparent 
negative heliotropic reaction by the germ-tubes was seen. The 
spores had been sown in a drop culture exposed to a unilateral illum- 
ination on a window sill and a high per cent, of the tubes had grown 
directly away from the light. Subsequent tests with controls in 
darkness substantiated the first observations. A search of the liter- 
ature brought forth a single mention of a heliotropic reaction in ger- 
minating rust spores. Ward,^ referring to a series of germination 
studies with urediniospores of Puccinia dtspersa, has written: "My 
reasons for varying the direction of incidence of the light in certain 
cases were based on some results (as yet inconclusive) that the 
germ-tubes exhibit heliotropic curvatures." 
That the sporidial germ-tubes of Puccinia malvacearum react 
negatively to daylight has been shown recently by Robinson,^ but 
aeciospore germ-tubes of Puccinia Poarum were found to be indifferent. 
Germ-tubes of conidia of Bottytis sp. also grew away from light but 
those of other non-rust fungi tested AUernatia sp., Penicillium glaucum 
and Peronospora parasitica, were indifferent according to Robinson. 
During the past fall, 1914, the study of the effect of light on germ- 
inating urediniospores of Puccinia Rhamni was again taken up. 
Urediniospores were obtained at first from the field and stored in 
gelatin capsules and later from cultures on oat plants grown in the 
greenhouse. The urediniospores of this species are especially suitable 
to daylight tests on account of their quick germination and the rapid 
growth of their germ-tubes. In the tests made the germ-tubes aver- 
aged in growth once to twice the spore length in as many hours and 
four to six times in three to four hours. 
^ Read before the American Phytopathological Society at the Philadelphia 
rneeting, January i, 191 5. 
2 Ward, H. M. Ann. Bot. 16: 267. 1902. 
2 Robinson, W. Ann. Bot. 28: 331-340. 1914. 
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