ON VINE MILDEW. 5 



a disease in the bark, and so derange the physiological functions 

 of the leaves, that the plant may for a time be prostrated, though 

 possibly the notion that the vine is irrecoverably lost may be prema- 

 ture. It is, however, difficult to judge of the matter at a distance. 



I proved by experiment during the course of this year, as in 

 Switzerland in the preceding season, that the fungus does not 

 spread from the vine to any other plant. Similar fungi, indeed, 

 occurred commonly on other plants, as on roses, partly before 

 the vines exhibited any symptoms of disease, but none of these 

 appeai'ed to me to be identical with Oiclium Tiickeri. 



As regards the connection indicated above of the fungus with 

 the cuticle of the green organs, and its power of producing 

 disease ; if clear notions on the subject are desired, we must not 

 choose for examination those parts which are thickly covered 

 with the fungus, but those in which it appears under the form of 

 a delicate arachnoid web, scarcely perceptible under a lens. It 

 is a matter of indifference, in this point of view, whether the 

 bark of the green branches be chosen, the tendrils, the peduncles 

 of the bunches, the integumeuts of the closed flower-buds, or the 

 young fruit of but one or two lines long, provided the leaves are 

 excepted. 



With respect to the extension of the fungus on its first appear- 

 ance, it must be considered as altogether local, for it occurs in 

 insulated specks, which send out radiating threads from their cir- 

 cumference, and so becoming confluent, gradually cover, more or 

 less completely, the surface of the organs which are attacked. 

 On the branches the parasite occurs regularly on the lowest 

 and oldest internodes ; large spots covered with the fungus 

 appear on these, and, at a later period, on the intermediate inter- 

 nodes, while the upper internodes (as is at present universally 

 the case here) are altogether free. The fungus often spreads 

 to the ovaries from the peduncles, which are ah'eady attacked 

 before the blossoms expand, since the threads of the Mycelium, 

 a short time after the corolla falls, creep over the nectary and 

 involve the berries, commencing at their base. Meanwhile new 

 centres of development arise from which the fungous web 

 commences, caused probably by the oval vesicles or spores, which 

 are produced at a very early period of growth upon the erect 

 threads, and which germinate very readily and ai'e found widely 

 dispersed over every part of the plant, as for instance on the 

 ovaries soon after the fall of the blossom, and then mixed with 

 pollen grains. 



