MILDEW AND BRAND. 63 



minence^ and therefore they are not easily over- 

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

 this species of thistle_, we have not yet found this 

 P'lcccima on any other plant. The spores are ellip- 

 tical^ 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 (Gentcmrea 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 {Serratiila tinctoria). The 

 spores are oval^ scarcely constricted_, and not attenu- 

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

 site plants than those above named are liable 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 Yie, as well as our elders and 

 betters^ knew the tubers of Bunium flexuositm. 

 Not then_, nor for many years after^ did we notice^ 

 or regard if we did notice^ the distorted radical 



