320 
POPULAR SCIENCE REVIEW. 
spores more elongated than those of the other corn-rust (fig. 
12), and not so bright in colour. By intermediate forms these 
two rusts pass insensibly the one into the other, so that it is 
sometimes difficult to distinguish them. Both have the spores 
clustered together in the pustules, at first (fig. 11) attached by 
their peduncles, but they soon become free, and are scattered 
like rust-powder over the plant. Adverting to the attack of 
rust upon the wheat crops to an unusual extent a few years 
since, the Bev. M. J. Berkeley wrote as follows : — 
We have seen rust more prevalent in white wheats, especially in the variety 
called Russian white, which has red smooth chaff, than we ever remember it. 
It is, however, confined to particular spots ; and while in one field not a 
single leaf is free, insomuch that a person walking through the wheat is 
completely painted with the spores, of a fine rust-red ; an adjoining field, 
separated only by a hedge, has not a rusty leaf. So long, however, as the 
rust is confined to the leaf, it is, we believe, perfectly harmless. The grain 
swells in spite of it, and the only effect is that the flag dies a little earlier, 
which is not undesirable when it is too luxuriant. If, however, it gets to any 
extent upon the chaff, much more if it attacks the seed itself, as is some- 
times the case, it is very mischievous. 
There is, indeed, a notion that rust is merely a form of mildew, and this 
may be true ; but if so, it is a harmless form. The true rust (T. rubigo 
vera ) if a form of mildew preserves its own characters to the end, and merely 
presents a second form of fruit, a circumstance which is exceedingly common 
amongst the lower fungi. It may exist in company with the mildew, but it 
also more frequently is developed without a trace of mildew intermixed. 
As far, then, as its immediate effects upon the plant 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 com- 
parison with such plants as marigold and orache, which produce seeds of 
two different forms. Its ultimate effects may, indeed, be injurious, 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, which is in fact merely 
the young state of the mildew. When once that supposed species makes its 
appearance, it is quite certain that 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 inter- 
mediate state of form and colour. 
M. Tulasne, to whom I have already alluded as a high 
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 (Lecythea ) , for the same reason, has shared the same fate; 
It must not be forgotten that twenty-five species of rust 
belonging to this genus have been recorded as occurring in 
Great Britain. Some of these have yellow or yellowish spores ; 
