POLYMORPHISM. 201 
some winter rye was sown round a berberry bush, which in the 
following year was infested with Atcidium, which was mature in 
the middle of May, when the rye was completely covered with 
rust. Of the wild grasses near the bush, Triticum repens was 
most affected. The distant plants of rye were free from rust. 
The spores of the Aicidium would not germinate on berberry 
leaves ; the berberry Acidium could not therefore spring from 
the previous 4icidium. The uredospores of Puccinia graminis 
on germinating penetrate into the parenchym of the grass on 
which they are sown; but on berberry leaves, if the tips of the 
threads enter for a short distance into the stomates their growth 
at once ceases, and the leaves remain free from parasites. 
Fic. 107.—Cells and pseudospores of Heidium berberidis. 
Montagne has, however, described a Puccinia berberidis on 
leaves of Berberis glauca from Chili, which grows in company 
Fic. 108.—Cells and pscudospores of Aeidium graveolens. 
with Aicidium berberidis. This at first sight seems to contradict 
the above conclusions; but the Aicidium which from the same 
disc produces the puccinoid resting spores, appears to be dil- 
ferent from the European species, inasmuch as the cells of the 
wall of the sporangium are twice as large, and the spores de- 
cidedly of greater diameter.* The resting spores, moreover, 
* We have before us an Acidium on leaves of Berberis vulgaris, collected at 
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