150 DISEASES OF FIELD & GARDEN CROPS. [CH. 



ing stems, and as they fall the faintest breath of air wafts 

 them away. 



If Uredo spores are kept in moist air for a few hours 

 they readily germinate. This germination usually takes 

 place by the protrusion of two germ tubes or threads of 

 mycelium, one from each side, usually near the middle, 

 and rarely from or near the top of the spore. The spots 

 whence the tubes are destined to emerge from the spores 



X-IOOO 



FIG. 75. 

 Spores of Uredo linearis, Pers. Enlarged 1000 diameters. 



can often be readily seen before germination takes place 

 as at BC, Fig. 75. These germinal spots are weak 

 places in the inner wall of the spore. Two spores, 

 enlarged 400 diameters, are shown germinating on a frag- 

 ment of the epidermis of a wheat plant in Fig. 76. 

 These two spores show the extreme limit of size. It 

 seldom happens that both germ tubes continue their 

 growth ; one usually remains effete, as at AA, whilst 



