te, and sometimes, in the younger leaves, the luxuriance was far
greater than in free nature. Similar plants, to the number of two
hundred, were observed in the nursery, and though some of them had
_AEcidium_ pustules, not one fresh pustule was produced; while two
placed under similar circumstances, but without the application of any
resting spores, remained all the summer free from _AEcidium_. It seems,
then, indubitable so far that _AEcidium berberidis_ does spring from
the spores of _Puccinia graminis_.

It has, however, to be remarked that De Bary was not equally
successful in producing the _Puccinia_ from the spores of the
_AEcidium_. In many cases the spores do not germinate when placed on
glass, and they do not preserve their power of germinating very long.
He reverts then to the evidence of experiments instituted by
agriculturists. Boenninghausen remarked, in 1818, that wheat, rye, and
barley which were sown in the neighbourhood of a berberry bush covered
with _AEcidium_ contracted rust immediately after the maturation of the
spores of the _AEcidia_. The rust was most abundant where the wind
carried the spores. The following year the same observations were
repeated; the spores of the _AEcidium_ were collected, and applied to
some healthy plants of rye. After five or six days these plants were
affected with rust, while the remainder of the crop was sound. In
1863 some winter rye was sown round a berberry bush, which in the
following year was infested with _AEcidium_, 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.

[Illustration: FIG. 107.--Cells and pseudospores of _AEcidium berberidis_.]

The spores of the _AEcidium_ would not germinate on berberry leaves;
the berberry _AEcidium_ could not therefore spring from the previous
_AEcidium_. 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.

[Illustration: FIG. 108.--Cells and pseudospores of _AEcidium graveolens_.]

Montagne has, however, described a _Puccinia berberidis_ on leaves of
_Berberis glauca_ from Chili, which grows in company with _AEcidium
berberidis_. This at f