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. 317, A and B, and Fig. 318). 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. 317, C). From 

 this last mycelium the secidium 

 fruits first described develop. 



(a) The life-cycle, as atove given, 

 is apparently abridged in Bnme of 

 tlie Uredlnese. Tlie secidium and uredo stages are merged into one, or 

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

 case in Phragmidium, Qymnosporangium, 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 alternation, which is termed by De Bary Jietercecism, has 

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

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

 in some instances be only an obscure heteroecism. 



(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 tlie reproductive organs of most complex struc- 



Fij?. 218.— Germinating; teleutospore 

 of Jhteeinia Molinix^ showing promy- 

 celium and eporidia.— After Tulasne. 



* '• Lehrbuoh der Botanik," 4te Auflage, 1874, p. 331. 



