UREDINEAE. 329 



sporidia on germination give infecting mycelial hypliae. In 

 the case of Coleosijoritdn, the promycelium is formed inside the 

 teleutospore in a manner similar to the Protobasidiomycetes. 



Besides teleutospores, there occur uredospores. These are 

 given off from patches or sori throughout the summer till 

 autumn, when they are followed by teleutospores on the same 

 sori. The uredospores somewhat resemble the teleutospores, 

 but generally consist of one cell only with a thinner coat of 

 lighter colour ; they either germinate at once without a resting 

 period, and give rise to a germ-tube capable of direct infection 

 of new hosts ; or less frequently they are resting-spores for 

 a time. 



A third form of spore occurring in the life-history of the 

 Uredineae is the aecidiospore, produced in a special structure, 

 the aecidium. The aecidium is developed inside the leaves or 

 other organs of the host-plant, and when mature ruptures the 

 overlying epidermis ; it has as a basis a firm liyphal tissue, 

 the upper surface of which becomes a disc of short erect sporo- 

 phores. From each sporophore there is formed by intercalary 

 growth a chain of cells consisting alternately of spores and 

 smaller intermediate cells, which do not become spores. The 

 youngest cells in an aecidium are those next the sporophore- 

 disc, and they are forced outwards by intercalation of younger 

 cells between them and the disc. The cells so produced 

 become alternately intermediate cells and spores ; the former 

 increase for a time, then decrease and disappear, the spores 

 liowever continue to increase in size as the chain grows forward 

 and to take on the characters of the mature aecidiospore till 

 they are finally shed from the aecidium. The production and 

 distribution of aecidiospores may thus go on continuously for 

 a considerable time. The sporophores at the periphery of the 

 disc do not however produce spores ; chains of cells are also 

 produced from them by intercalary growth, but the cells are of 

 equal size, and remain closely connected with their neighbours, 

 so as to form a membranous covering over the spore-sorus, 

 this is the so-called peridium, on rupture of which the aecidio- 

 spores escape. In many Uredineae the peridium is suppressed 

 (Cncoma) ; in others {Phrafjmidium) it is replaced by other 

 structures, the paraphyses. The spores of the genus Endophyllnm 

 are produced in series in aecidia enclosed by a peridium, but in 



