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ity, but they domuch to weaken the growth and keep them in check. 
The Canada thistle rust, mentioned in the last report of the Station,* 
usually prevents the formation of seeds, and permits the plant to 
make but a feeble growth. Some seasons at least its activity must 
be an item of considerable moment, and as it is not known to in- 
habit other plants in this country, it is to be encouraged. A less 
effective parasite of the same plant is the white rust (Cystopus cubi- 
cus Léy.), which forms white blister-like patches on leaves and stems, 
of irregular shape but usually elongated, and an eighth of an inch 
or more long. It is not confined to the thistle as in the case of the 
dark rust, but attacks several related plants such as the rag weed and 
wild wormwood. It was also found this season in unpleasant abund- 
ance on our beds of salsify, giving the foliage quite a spotted and 
whitened appearance. A surface mildew (Erysiphe lamprocarpa) 
makes a white cobwebby mould over several kinds of thistles, cockle- 
bur, various stick-tights and other noxious weeds. 
Another one of the white rusts (C. Portulace Lév.) is confined to 
the purslane, and the cultivator should look upon its white mottling 
with the reflection that even this audacious and over corpulent plant 
has its natural enemies. 
The pigweed, the one whose tender foliage is sometimes eaten for 
greens, 1s beset by a number of fungous enemies, which spot and rid- 
dle its leaves, besides a Peronospora (P. effusa Rabh.) which often 
takes enough of its nourishment to considerably enfeeble the plant. 
This Peronospora does not induce rot as in the case of the nearly re- 
lated forms on lettuce and potato, but builds patches of dirty white 
felt on the underside of the leaves on which the spores are produced. 
The redroot, which also takes the name of pigweed in many local- 
ities, has a white rust of its own, and is also infested with Various 
microscopic fungi which taken together result in no slight drain 
upon its forces. And so we might continue through the whole list 
of weeds, each would be found to be beset by its natural enemies, 
which in many cases are confined to them alone, or only spread to 
plants which are not especially prized by the cultivator. It is evi- 
dently well to bear in mind that the parasitic fungi are not all bad, 
but that some are even beneficial by preying upon troublesome plants 
and insects; recognition of one’s friends is also a desirable thing, and 
hence the wisdom of giving some attention to the identification of 
such parasites and to their habits of life. 
*Third An. Report, p. 385. 
