EUSTS. 97 



go, it may be treated as a distinct parasite, though advanced 

 botanists may look upon it as offering a case of what they call 

 dualism, which may be easily understood on a comparison with 

 such plants as marigold and orache, which produce seeds of 

 two diflferent forms. Its ultimate effects may, indeed, be inju- 

 rious, as, if it be really a second form of mildew, it is capable 

 of propagating that pest. The case is quite different with 

 Trichobasis linearis, wliich is in fact merely the young state of 

 the mildew. When once that supposed species makes its 

 appearance, it is quite certain tJiat there will be mildew to a 

 greater or less extent. While the spores of the one remain 

 unaltered, though intermixed with the true bipartite spores of 

 the mildew, the other exhibits every intermediate state of form 

 and colour. 



M. Tulasne, to wliom we have already alluded as 

 a liigh authority on this subject,, is of opinion that 

 all the species enumerated in this group or genus, 

 are mere conditions of other species, and therefore 

 excludes it altogether. Another genus {LecytJiea), 

 for the same reason, has shared the same fate. 



It must not be forgotten that twenty-eight species 

 of rust belonging to this genus are now recorded 

 as occurring in Great Britain. Some of these have- 

 yellow or yellowish spores ; the rest have the spores 

 of a decidedly brown colour. One of the most 

 attractive of the yellow-spored species is that which 

 appears on the groundsel {T. Senecionis), and a 

 good notion of its external appearance may be 

 gained from our figure (plate VII. fig. 145). It is 

 not always to be found without searching closely, 

 for in some localities we have found it very spar- 

 ingly, whilst elsewhere — as, for instance, on Wands- 



n 



