384 



UREDINEAE. 



spores grow on needles and twigs of Coniferae, the aecidia on 

 the leaves of various Eosaeeae (Pomaceae). Five species occur 

 in Germany, but there are many in America. 



Gymnosporangium clavariaeforme Jacquin. (Britain and 

 U.S. America.) The mycelium of this species perennates in 

 twigs of Juniperus communis. Infection is brought about by 

 aecidiospores. In the following year a swelling of attacked 

 places is evident, and this increases till death of the host 

 ensues. In spring, about the beginning of April, little Hght- 

 yellow cone-like .structures break out on the swollen places. 



ilh 



Fig. 217. — Section through a swelling on a sixteen-year twig 

 of J Juniper attacked by Gymnosporangium in its eighth year; 

 three conical spore-cushions !u*e Indicated, also a cushion-scar 

 with the scar-tissue. (After Woemle.) 





Fig. 21S. — Longitudinal 

 section of a spore-cashion 

 of Gymnospoitingium da' 

 vai-ia^'orme. Somewhat 

 diagrammatic (After 



Woemle.) 



and during rain swell up into long club-shaped sporophores, 

 containing long-stalked, spindle-shaped teleutospores, some thick- 

 coated, some thin. The sporophores swell and ultimately form 

 a common mass in which the teleutospores germinate. The 

 spores have four germ-pores, each capable of giving ofif a 

 promycelium with pointed sterigmata producing sporidia, which 

 are cast loose and distributed by wind. 



Germination of sporidia takes place on leaves, cotyledons, 

 petioles, and shoots of various Pomaceae, where they may 

 induce swellings or curvature, often to a considerable extent. 



