MILDEW AND BEAND. 63 



minence, and therefore they are not easily over- 

 looked (plate lY. fig. 63). Although not confined to 

 this species of thistle^ we have not yet found this 

 Puccinia on any other plant. The spores are ellip- 

 ticalj rather elongated, constricted, and without 

 spines (fig. 64). 



Other species of Puccinia are found on Composite 

 plants, but with none of these is the present fungus 

 likely to be confounded, if regard be had to its 

 peculiar habit. The leaves, for instance, of the 

 common knapweed {Centaur ea nigra) are often 

 sprinkled with the small pustules of the centaury 

 brand {Puccinia compositarum, Sch.) ; these generally 

 occupy the under surface of the lower radical 

 leaves (fig. 67) ; occasionally a few of the pustules 

 appear on the upper surface. We have not often 

 found this fungus in the neighbourhood of London 

 on the leaves of the knapweed, but, on the other 

 hand, we have encountered it very commonly on 

 those of the saw-wort {Serratula tinctoria). The 

 spores a^B oval, scarcely constricted, and not attenu- 

 ated in either direction (fig. 68). Other Compo- 

 site plants than those above named are hable to 

 attacks from this parasite. 



In our school-days we remember to have spent 

 many a stray half-hour digging for " earth-nuts," 

 under which name we, as well as our elders and 

 betters, knew the tubers of BuniuTn flexuosum. 

 Not then, nor for many years after, did we notice, 

 or regard if we did notice, the distorted radical 



