RUSTS. Ill 



presence of the fungus. The microscopical features 

 of the spores of this genus are, briefly, a more or 

 less spherical form, without any pedicel or footstalk 

 -(plate VII. fig. 134). These spores are at first 

 produced each in a separate cell, but when ripe 

 become free, and are at times with diSiculty dis- 

 tinguished from such forms as TricJiohasis, unless 

 the pedicels in the early stage of the latter genus 

 are regarded. 



A rare species in Britain is the oak-leaf rust 

 (Uredo Quercus), in which the sori or pustules are 

 ■minute, and at first yellow, but afterwards orange. 

 It occurs on the under surface of the leaves, and 

 was, we believe, first found in this country by Mr. 

 D. Stock, in the neighbourhood of Bungay, nearly 

 five -and -thirty years since. That gentleman in- 

 formed us that it was not at all uncommon, but 

 always appeared on the young shoots which had 

 sprung up from the trunks or roots of trees that 

 had been cut down. It has been found by several 

 other persons since that time in this country, and 

 it is not uncommon in France. 



The leaves of the common sorrel are often 

 sparely sprinkled with the pustules of a rust 

 {Uredo bifronSj Grev.), which derives its specific 

 name from the fact that the pustules, which appear 

 on both surfaces of the leaves, are often opposite 

 to each other (plate YII. fig. 137). These pustules 

 are generally seated on a discoloured spot (plate 

 YII. fig. 138 enlarged), and are surrounded by the 



