116 MICEOSCOPIC FUNGI. 



The under surface of tlie leaves of the white 

 Dutch clover are often sprinkled with black spots^ 

 which are nearly round and very numerous. These 

 are so many clusters of fungi belonging to a 

 diflTerent section_, in which the threads are the 

 important feature. But another parasite is also 

 found on leaves of the same plant_, in which the 

 pustules are far less numerous and regular^ and 

 are often found on the petiole as well as the leaf^ 

 distorting them and twisting them in various direc- 

 tions (plate VII. fig. 154). This is the clover rust 

 {Uromyces apiculatay Lev.)^ which is a parasite on 

 numerous plants^ being found also on the great 

 water- dock and other kinds of dock. The spores 

 are ovoid and brown^ with a short peduncle (plate 

 VII. fig. 155). A very beautiful species occurs on 

 the leaves of the ladies-mantle {Alchemilla), but 

 hitherto we have not been fortunate enough to 

 collect it. 



It can scarcely be too great an assumption to 

 suppose that every one is acquainted with the goat- 

 willow [Salix capreajy or that every schoolboy 

 knows the birch {Betiila alba). It may be pro- 

 ceeding a step too far to affirm that all who know 

 these trees well enough to distinguish the one from 

 the other^ will have observed the under surfaces of 

 the leaves of both sprinkled with a golden dust^ 

 during the summer months^ and which are the 

 spores of a parasitic fungus. So common is this 

 orange-coloured powder on leaves of the trees 



