14 



All proceed from extremely minute bodies, termed spores, 

 so small that thousands have to be placed in line to attain 

 the extent of an inch, and are, therefore, singly quite 

 invisible to the naked eye. Again, they are produced in such 

 inconceivably large numbers that millions are said to be 

 evolved from a single plant. Some float in the air constantly, 

 and at all heights, assisting — Prof. Huxley suggests — in causing 

 the blueness of the sky. Thus they are spread over the world, 

 only awaiting a favourable opportunity to alight on a suitable 

 host, where they germinate, grow, and give birth to millions 

 more. Ordinary terrestrial heat little affects these spores, but 

 myriads perish by moisture and warmth, causing germination 

 when not near or upon a congenial plant ; or the temperature 

 may be below the limit proper to their development ; or the 

 cuticle of the plant maybe too hard or too tough to be penetrated, 

 for fungoids of this class only develop within the tissues of 

 their hosts. Before describing the manner of the germination 

 of spores, which differs widely from that of seeds proper, it 

 must be remarked that many fungoids, as well as numerous 

 animal parasites of low organization, undergo a two-fold 

 development known as " alternation of generation," or 

 " metagenesis," to which our Red Rust very probably is also 

 subject. In this the rule that " like produces like " does not 

 hold good, the spores of a fungus of definite forms infecting 

 one plant not propagating upon the same, but upon a totally 

 different one, and developing into a growth more or less dif- 

 ferent from its progenitor. The spores of this last, however, 

 return to the former host and produce the original fungus in an 

 analogous matter to "measles" in pork, entering the human 

 frame and developing into the tapeworm, while the eggs of the 

 latter swallowed by pigs infect them with measles. The best 

 known instance of this, according to some authors, is that of 

 the "foetid smut" — Tilletia caries (Uredo fcetida) — which is 

 said in its second form to propagate upon JBerberis vulgaris, L., 

 the eradication of this shrub in the vicinity of cornfields being 

 followed by almost total disappearance of the said smut. The 

 Red Rust appearing to belong to this class of fungoids, its 

 second host is seemingly the so-called "barley grass," an intro- 

 duced plant — (other grasses, several acacias, especially a species 

 with greyish-green velvetty leaves growing near Callington, 

 Truro, &c, are likewise strongly suspected) — which of late 

 years has largely supplanted the native grasses, and upon 

 which the rust appears before any other plant in the form of 

 numerous brownish spots upon the leaves. This generally takes 

 place in July, August, or September, sometimes earlier, some- 

 times later, according to the general temperature of the season. 

 Should the ground be very moist, the weather at the time be 



