PARASITIC FUNGI AND MOULDS. 17 
the complete development of the fungus is only effected 
by its transference from one plant to another. This 
phenomenon may be frequently observed in animal 
and vegetable parasites, and it seems to be designed 
in order to secure the preservation of the parasitic 
species, by permitting it to grow on two plants in 
succession, of which the development occurs at different 
periods of the year; such is the case with the barberry, 
which is developed in early spring, while wheat is 
developed in summer. For a long while it was 
believed that Gcidiwm berberidis, Uredo linearis, 
and Puccinia graminis were so many distinct 
species; but it is now known, as we have stated, 
that they are only three successive phases of the 
development of a single species.* 
Other Uredinee, constituting the modern varieties 
of Ustilago and Tilletia, are more apt to affect the 
ears of wheat and other grasses. This disease is termed 
by agriculturists smut or caries (Uredo carbo or 
Ustilago segetum, and Tilletia caries). The diseased 
grain merely appears to be of a somewhat darker 
colour, but on pressing it between the fingers, there 
issues from it a blackish, oily pulp, which smells 
like rotten fish. Bread made from the flour of such 
corn has an acrid and bitter taste, and although it 
does not appear to be directly injurious to health, 
* So, again, Ecidium rhamni (Nerprun or Bourdaine) produce 
Uredo rubigo-vera and Puccinia coronata of wheat and cats. (See 
Fig. 7.) 
