286 OBSERVATIONS ON THE VINE MILDEW. 



foliage of our trees ? Not a leaf would preserve its integrity ; 

 all would be diseased. Much more must accidental productions 

 bear some proportion to the size of the insects ; but this is not 

 the case ; and by a kind of eccentricity which is not rare in the 

 human mind, we refer to the most minute causes, the most mani- 

 fest effects ; a locust may pass over without leaving any traces, 

 where those which a plant-louse causes are indelible. 



I repeat, then, that the vine Hrineum does not depend on the 

 puncture of an insect, but is an elongation of the epidermal 

 cells, due to some unknown cause, which exists in tiie plant 

 itself, as is also proved by the fact that the leaves while still 

 rolled up and plaited exhibit traces of the affection. 



I have said enough to enable any one to recognise the Erineum, 

 but to prevent its being confounded with Oidium Tuckeri I 

 think it right to call to mind the description which I gave of 

 thai mould last year, before the Societe Philomathique (1850, 

 August 3). 



The plants on which the mould is developed present the same 

 appearances as others, except tliat the shoots of the year, the 

 leaves, bunches, berries, and stamens, in a word all the diseased 

 parts, are covered with a very thin white pulverulent down, 

 which is visible at some distance, and which diffuses a very per- 

 ceptible mouldy smell. It forms on the leaves white circum- 

 scribed spots, which resemble those of Enjsiphe. This down, 

 when examined under the microscope, is formed of slender 

 branched articulated threads, which creep over the surface of the 

 leaves. From different points of this primitive mycelium spring 

 little erect straight stems, which are transparent, simple, and 

 articulated, and which bear at their extremity three, four, or 

 five, oval or elliptic simple hyaline spores, joined end to end like 

 the beads of a necklace, and filled with extremely fine granules. 

 These granules, when forced out by compression between two 

 plates of glass, are spherical, transparent, and endowed with 

 molecular motion. 



These characters do not leave room for any confusion. One 

 of these productions is confined to the under surface of the vine- 

 leaves ; it is persistent, and does not disappear Avhen rubbed : 

 the other, on the contrary, attacks every part of the vine except 

 the old branches and roots ; it is only temporary, and disappears 

 on the slightest friction. 



In questions of the diseases of the Vine, however, the Erineum 

 seems to bear a certain part. At least this was the case in 1835, 

 when M. Duby comnmnicated to the Natural History Society of 

 Geneva his observations on Torula dissiliens, which occasioned 

 the premature fall of the leaves of the vines in a great part of 

 the valley of the Leman Lake. M. Vallot, of Dijon, tiiought 



