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TRANSACTIONS OF TIIK ILLINOIS 



minute depredator, known as Stilhon vaporarium, B. and Br., belonging 

 to the same general order, but quite a different family. It was the subject 

 of a note in a former paper to this Society. Sulphur here again is of no 

 avail. Light, air, and a decrease of temperature are uniformly efficacious. 

 Leaf Blights. — Among the fungi properly known as leaf blights, 

 there is a class of plants which never penetrate the tissues, but live upon 

 the surface, deriving their nourishment in some way by simple contact. 

 The most of these belong to the old genus Oidiiim, but are now known 

 to bear other fruit bodies, which place them in the family Perispriacece, 

 the supposed Oidium plants only being a first stage of the latter, as the 

 caterpillar is the first form of the butterfly, yet evidently the same indi- 

 vidual, and so, most certainly the same species. If caterpillars laid eggs, 

 and thus gave origin to other caterpillars, as well as changed to butter- 

 flies, the example would be more appropriate. 



Rose Blight. — Rose leaves are often covered by a white, cobwebby 

 mildew or mould, and the tender stems are frequently distorted by the same 

 parasite. After the latter has attained some age, it becomes a tough felt, 



which can be separated from the leaves, 

 leaving tlie latter perfectly whole, showing 

 pretty clearly the surface character of the 

 fungus. The felted mass of threads is very 

 white and clear, under the microscope ap- 

 pearing of a pearly luster, often branching, 

 and giving rise here and there to upright 

 filaments, which gradually change their form 

 to a necklace-like chain of spores, by constric- 

 tion at regular intervals of the walls. The 

 uppermost ones become perfectly oval, and, 

 soon falling off, germinate anew, perhaps on 

 new territory. This is the Oidium stage; it 

 is shown at A, Fig. 2. Later, little dark specks 

 may be seen by the unaided eye upon the 

 same white threads. The specks are less than 

 the period mark on the printed page. Mag- 

 nifying these, we find they are globes with a 

 cellular or network-like surface, and bear 

 numerous white arms or heavy threads distinct 

 from the mycelium of the plant. Placing one 

 or two of the globes between two pieces of 

 glass, and pressing slightly upon them, they 

 are easily broken, and a thin, trans.parent sack, called spore case or 

 sporangium, is squeezed out, containing numerous spores. Some idea 

 of the appearance of the specks (peridiaj may be inferred from B, Fig. 2, 

 and of the spore case with spores from C, Fig. 2. The spores of the first 

 kind seem to be for the immediate propagation of the plant ; the second 

 for passing the winter. The name is Sphcerotheca parrnosa, Lev. 



Pea Mould. — Garden peas and beans, in autumn, often suffer from 

 Erysiphe Martii, Lk., a plant allied to the above. Not a garden in lUi- 



Fig. 2. Rose Mould. 



