It has, however, to be remarked that De Bary was not equally successful in producing the _Puccinia_ from the spores of the _Æcidium_. 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. Bönninghausen remarked, in 1818, that wheat, rye, and barley which were sown in the neighbourhood of a berberry bush covered with _Æcidium_ contracted rust immediately after the maturation of the spores of the _Æcidia_. The rust was most abundant where the wind carried the spores. The following year the same observations were repeated; the spores of the _Æcidium_ 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 _Æcidium_, 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 _Æcidium berberidis_.] The spores of the _Æcidium_ would not germinate on berberry leaves; the berberry _Æcidium_ could not therefore spring from the previous _Æcidium_. 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 _Æcidium graveolens_.] Montagne has, however, described a _Puccinia berberidis_ on leaves of _Berberis glauca_ from Chili, which grows in company with _Æcidium berberidis_. This at first sight seems to contradict the above conclusions; but the _Æcidium_ which from the same disc produces the puccinoid resting spores, appears to be different from the European species, inasmuch as the cells of the wall of the sporangium are twice as large, and the spores decidedly of greater diameter.[Z] The resting spores, moreover, differ not only from those of _Puccinia graminis_, but from those of all other European species.