VIII. On the structure and life-history of entyloma ranunculi (bonorden)
The attention of mycologists has been long directed to the study of the Ustilagineæ, not only on account of their morphological peculiarities, but even more especially because the economic questions arising from their relations to our crops, &c., have assumed such proportions as to force this group of parasites far into the foreground. Interesting and important as are the parasitic habits of the Ustilagineæ, however, and much as they have been investigated, it has to be admitted that we know as yet very little about them. Two or three of the most common forms, it is true, have been so often studied by different observers that they may be regarded as worked out sufficiently to allow of our regarding them as types; but it needs no very extensive acquaintance with the group to satisfy ourselves that the best known forms are not the simplest, and that much still remains to be accomplished in this large group. It is not only that the Ustilagineæ are so minute, but they are so peculiarly modified, and so specialised as parasites, that the most careful observation is necessary in making out the numerous points in their structure; in addition, observers still differ considerably as to the interpretation of some of the facts of structure which are established. Taking the most recent systems of classification, we may regard the Ustilagineæ as comprising the following genera, Ustilago,Tillertia, Urocystis, Schizonella , and Entyloma , and so far shall be in accordance with all the modern authorities; when we come to such genera as Geminella,Sphacelotheca, Doassansia (Cornu), and Graphiola (Fischer) and some others, the matter becomes more complicated, and special investigations are still needed to determine the limits of the genera and group. Entyloma , however, is a well-established genus, and now includes some fifteen or sixteen species. They are parasitic in the mesophyll of the leaves of various plants, and are characterised by producing rounded resting-spores as intercalary swellings on the very fine, septate, intercellular mycelium; these spores germinate like those of Tilletia . In Tilletia , however, the resting-spores form dense powdery aggregates, which is not the case with the more isolated spores of Entyloma .