EUSTS. Ill 



presence of tlie fungus. The microscopical features- 

 of tlie 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 ceU, but when ripe 

 become free^ and are at times with difiiculty dis- 

 tinguished from such forms as Trichohasis, 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- twenty years since. That gentleman in- 

 forms 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. We are uncertain whether it 

 has been found by any one since that time in this 

 country, although it is not uncommon in France. 



The leaves of the common sorrel are often 

 sparely sprinkled with the pustules of a rust 

 (Uredo hifronSj 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 tho 



