384 



UREDINEAE. 



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

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

 in Germany, but there are many in America. 



Gymnosporangium clavariaeforme Jacquin. (Britain and 

 U.S. Anu-rica.) Tlie 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 light- 

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



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

 of Juniper attacked by Gymnosporangium in its eighth year; 

 three conical spore-cushions are indicated, also a cushion-scar 

 with the scar- tissue. (After Woemle.) 



Fig. -ils. — Lmigitudiual 

 section of a spore-cushion 

 of Gymnosporanqhnn eld- 

 vnriitcforme. Somewhat 

 diagrammatic. (After 



Woernle.) 



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 off a 

 promyceliuin 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. 



