314 



BOTANY. 



or less elongated lines. In color they are almost invariably 

 brown or nearly black,in marked contrast to the reddish yellow 

 (orange) uredospores. In some cases they are produced early 

 in the season, but in the greater number of cases they appear 

 in the autumn, and then remain through the winter upon 

 the dead stems of their host plants. The following spring 

 the teleutospores germinate by sending out a jointed filament 

 (the promycelium) from each cell ; this grows to several times 

 the length of the teleutospore, and then sends out a few lateral 

 branches, each of which bears a small terminal cell, a sporid- 

 ium (Fig. 217, A and B, and Fig. 218). The sporidia are 

 extremely minute, and, as a 

 consequence, are carried about 

 from place to place in the wind 

 with great ease. When they 

 fall upon the proper plant, each 

 sporidium sends out a minute 

 filament, which perforates the 

 epidermis-cells, and from these 

 passes into the leaf parenchy- 

 ma, where it develops into a 

 mycelium (Fig. 217, C). From 

 this last mycelium the aecidium 

 fruits first described develop. 



Fig. 218. Germinating teleutocpore 



of tfwtinia Molinut, showing promy- (a) The life-cycle, as above given, 

 celium and sporidia. -After Tulasne. J8 ap p are ntly abridged in some of 

 the Uredineae. The secidium and uredo stages are merged into one, or 

 either the first or second is entirely wanting. This appears to be the 

 case in Phragmidium, Gymnoaporangium, Melampsora, etc. 



(6) With most of the species it happens that the secidiospores (conidia) 

 develop upon one host, and the uredospores and teleutospores upon an- 

 other. This alteruation, which is termed by De Bary hetercecism, has 

 added very much to the difficulty of the study of these fungi, and pos- 

 sibly the apparent abridgement of the life-cycle above mentioned may 

 in some instances be only an obscure hetenBcisin. 



(c) Thus far the sexual organs have not been discovered ; Sachs* 

 argues that they must precede the secidiospores, and that the secidium 

 fruit is in all probability the result of a sexual act. He bases his argu- 

 ment upon the law that the reproductive organs of most complex struc- 



* Lehrbnch der Botanik," 4te Auflage, 1874, p. 331. 



