140 DISEASES OF FIELD & GARDEN CROPS. [CH. 



developed in the autumn, they will not, as a rule, 

 germinate till the following spring ; they then burst in 

 the manner illustrated at Fig. 69, enlarged 1000 dia- 

 meters, upon old decaying grass and straw upon the 

 ground. In the warm damp weather of April and May 

 one or both segments of a teleutospore will burst and 

 produce a transparent thread of mycelium, termed by 

 botanists pro-mycelium, because it is the first mycelium 

 of a cycle of phenomena belonging to Puccinia. The 

 compound teleutospore is shown at AA, with its short 

 stalk B still attached. As the pro-mycelial threads, CO, 



Fig. 68. 



Transverse section through a pustule or Sorus of Puccinia Rubigo-vera, D.C. 

 Enlarged 200 diameters. 



increase in length, the protoplasm pours from the spores 

 into the tubes. A series of septa then appear, two of 

 which are seen at DD, and these septa enclose the 

 protoplasm in the growing end of the tube ; from this 

 end two or three minute transparent or pale yellowish 

 spores, termed pro -mycelium spores, as at EEE, are 

 borne : these speedily fall from their slender supports, 

 and germinate very readily on damp surfaces, as shown 

 at F. 



It might be considered reasonable to suppose that these 

 little pro -mycelium spores, as produced in the spring, 

 would, if placed on the leaves of grasses, reproduce the 

 Uredo first described ; but many botanists believe it to be 

 proved that they do not and cannot at once reproduce the 

 Uredo ; but when placed on the leaves of certain plants 



