GARPOPHYTA. 193 



ried away by the winds. This stage is known as the 

 cluster-cup stage. 



354. (II) The conidia falling upon a wheat-leaf germi- 

 nate there and- penetrate its tissues, sending parasitic fila- 

 ments into the cells. After a few days, if the weather has 

 been favorable, the parasite has grown sufficiently to begin 

 the formation of large reddish spores (stylospores) just be- 

 neath the epidermis, which is soon ruptured, exposing the 

 spores (Fig. 113, //) in reddish lines or spots upon the 

 leaves and stems. This is the Eed-rust stage, so common 

 before wheat-harvest. These red spores fall easily, and 

 quickly germinate (Fig. 114, D), producing more Red Eust 

 and so rapidly increasing the parasite. 



355. (Ill) Somewhat later in the season the same para- 

 sitic filaments which have been producing Red-rust spores 

 begin to produce lines or spots of dark-colored, thick- 

 walled, two-celled bodies constituting the Black Eust (Fig. 

 113, III). These are the " teleutospores " of the older 

 books, but they are here regarded as spore-sacs, each con- 

 taining two spores. The wall of the spore-sac fits tightly 

 over the relatively large spores. We may well retain the 

 name teleutospore for the spores within the sac. Being 

 thick- walled, these spores endure the winter without injury, 

 and when spring comes (IV) they germinate on the rotting 

 straw and produce several minute spores, called sporids 

 (Fig. 114, A and B). This is the fourth and last stage of 

 the rust. The sporids fall upon Barberry-leaves and germi- 

 nate (Fig. 114, 0), giving rise to cluster-cups again. 



These stages are so different in appearance that for a long time 

 they were regarded as distinct plants, and received different names. 

 Thus the first stage was classified as a species of Aecidium, the 

 second as a species of Uredo, and the third as a Puccinia. We still 

 preserve these names by sometimes calling; the spores of the first 



