FUNGOID PESTS OF CULTIVATED PLANTS. 



121 



a small cluster of flask-shaped pale brown bodies called peridia, and these 

 are soon split lengthwise nearly to the base into thread-like filaments 

 which are for a long time united together at the apex. The contents of 

 these flask-shaped bodies are the aBcidiospores, which are nearly globose 

 and warted on the surface (25-40 x 18-25 ju). These spores are produced 

 in chains, readily separating from each other. 



Spots are also to be seen on the opposite side of the leaf to that which 

 bears the Rcestelia and corresponding to it. These are conspicuous by 

 their orange colour, which becomes reddish, sprinkled with blackish dots, 

 which indicate cells containing very minute bodies called spermatia, which 

 are expelled when mature. 



It is recorded in Hooker's "British Flora" that when young Pear 

 trees are planted near old trees suffering from the Rcestelia the young 



FIG. 16. PEAR-LEAF CLUSTEB-CUP. 



A fungus growing on two different kinds of plant at different periods of its 



life-cycle. 



1. The spring stage of the fungus on a living Juniper branch, reduced in size. 

 2. Spore of same, x 300. 3, 4. " Cluster-cup," or summer form of fungus 

 fruit on living Pear leaves, reduced in size. 5. Two cluster-cups, one cut 

 open, slightly x . 6. Spores of cluster-cup condition, x 300. 



trees have been observed to become much injured by the fungus. Mr. 

 Knight sowed Pear seeds in soil infested with Bastelia, and the very 

 youngest of the seedlings showed the disease. 



According to theory it is contended that this kind of cluster-cups 

 must also have a condition analogous to the Uredo and Puccinia forms. 

 As this is not known to take place upon the Pear tree itself, it is inferred 

 that it must take place upon some other plant. The plant selected as 

 fulfilling the condition is the Savin, and it is contended that the cluster- 

 cups of the Pear tree produces those gelatinous exudations on the stems 

 of the Savin which are known under the name of Gymnosporangium. 



(Ersted originated this suggestion in 1865, when he intimated that he 

 had learned that gardeners were of opinion that the Pear fungus was 

 never seen except after the appearance of the fungus on Savin. Hence 



