196 



their distribution. Now as the season progresses, the myce- 

 lium which, for some weeks, has only produced uredospores, 

 now begins to form a totally different kind of spore, which 

 are known as teleutospores. These, instead of being orange or 

 reddish in colour, are dark purple -brown or black, and their 

 formation can be recognized by the appearance of grey streaks 

 and patches among the orange ones which spread and get darker 

 in colour, until ultimately the black pustules entirely replace the 

 rust- coloured ones which preceded them [see Plate XIX (1)]. 

 These teleuto -spores are formed in the same manner as the uredo- 

 spores and by the same mycelium, the latter in the beginning 

 of the season producing only uredospores, then later a few 

 teleutospores among the uredospores, and ultimately nothing but 

 teleutospores. These spores which are formed by the fungus 

 in the later stage of its life-history, besides being quite distinct 

 in appearance from the uredospores, have a different function, 

 they being virtually resting spores. Besides the difference in 

 colour, each teleutospore instead of being one-celled is divided 

 across the middle into two cells or chambers. They are more 

 elongated and club-like in shape and have a thicker wall. They 

 are also as a rule not shed so quickly as the uredospores but 

 remain firmly attached to the wheat straw. They are generally 

 incapable of germinating for some months after their formation. 

 When they do germinate each cell sends out a short hypha 

 which then becomes divided by cross partition walls into 

 segments. From each segment a short lateral stalk (sterigma) 

 is produced, the tip of which swells and then falls off the 

 minute, ovoid, spore-like bodies so formed being called sporidia. 

 The short hyphal filament developed from the teleutospore is 

 known as the promycelium. See Plate XIX (3). 



Now in Europe it was found that these sporidia could only 

 develop if placed on a new host-plant, a species of Berberis, i.e. 

 an altogether distinct species from that on which the teleuto- 

 spores were formed. Germinating then on the leaf of a suitable 

 host-plant, these sporidia send out their germ tubes which 

 directly pierce the leaf -tissue of the Berberis and develop a 

 parasitic mycelium within it, the mycelium deriving its nourish- 

 ment from the cells of the Berberis tissue. Although the 

 Berberis plant is thus more or less injured, the damage done is 

 usually nob severe, and the great practical importance of this 

 fungus depends on the injury done to the wheat plant, which 

 resubs in an enormous decrease in the yield of grain. The 

 presence of the mycelium in the Berberis induces swellings in the 

 leaf tissue on which two different kinds of spores are produced. 



