functions, these two kinds of spores have received different names. Those first produced have numerous papillæ on them, and were called _Uredospores_, from their analogies with the uredospore of the rust of wheat; the second kind of spore is smooth, and is called the _Teleutospore_, also from analogies with the spores produced in the late summer by the wheat rust. The fungus which produces these uredospores and teleutospores was named and has been long distinguished as _Coleosporium Senecionis_ (Pers.) We are not immediately interested in the damage done by this parasite to the weeds which it infests, and at any rate we might well be tempted to rejoice in its destructive action on these garden pests. It is sufficient to point out that the influence of the mycelium is to shorten the lives of the leaves, and to rob the plant of food material in the way referred to generally in my last article. What we are here more directly interested in is the following. A few years ago Wolff showed that if the spores from the _Æcidia Peridermium Pini_ (var. _acicola_) are sown on the leaf of _Senecio_, the germinal hyphæ which grow out from the spores _enter the stomata of the Senecio leaf, and there develop into the fungus called Coleosporium Senecionis_. In other words, the fungus growing in the cortex of the pine, and that parasitic on the leaves of the groundsel and its allies, are one and the same: it spends part of its life on the tree and the other part on the herb. [Illustration: FIG. 35. A spore of Peridermium Pini germinating. It puts forth the long, branched germinal hyphæ on the damp surface of a leaf of Senecio, and one of the branches enters a stoma, and forms a mycelium in the leaf: after some time, the mycelium gives rise to the uredospores and teleutospores of Coleosporium Senecionis. (After Tulasne: highly magnified.)] If I left the matter stated only in this bald manner, it is probable that few of my readers would believe the wonder. But, as a matter of fact, this phenomenon, on the one hand, is by no means a solitary instance, for we know many of these fungi which require two host plants in order to complete their life history; and, on the other hand, several observers of the highest rank have repeated Wolff's experiment and found his results correct. Hartig, for instance, to whose indefatigable and ingenious researches we owe most that is known of the disease caused by the _Peridermium_, has confirmed Wolff's results.