ON A'INE MILDEW, 



earliest state of the fungus on the bark of the branches and 

 tendrils, or on the young fruit. These organs appear after various 

 degrees of the evolution of the fungus, perfectly green, but for the 

 most part uumerous brown specks are visible on the organs 

 affected by the fungus even with the naked eye, but more cer- 

 tainly with a lens. Such specks must be chosen for examination, 

 for those parts which are iu a more advanced stage of decay, in 

 which the specks have become enlarged, are useless for this 

 purpose ; in consequence of which, iu my earlier investigations, in 

 which I had before me the later stages of disease, the relations in 

 question were not satisfactorily explained. Thus much is now 

 clearly established : amongst the youngest threads of Mycelium, 

 where they radiate on all sides from the margin of the spots, the 

 cuticle retains its normal green ; amongst the older parts of the 

 threads, on the contrary, little brown specks (Fig. 1 & '3,a a) are 

 visible. That this appearance is not accidental (for indeed the 

 dead and fallen hairs, for example, on the under side of the nerves, 

 leave little specks) is at once clear, when a part of the cuticle is 

 placed under the microscope, already covered with the network of 

 the threads of the Mycelium, for iu this case the dots occur with 

 the greatest regularity only beneath the threads of the fungus, 

 and therefore arranged after the fashion of a net. A good lens 

 will exhibit this phenomenon, but perfect conviction can be 

 obtained only by means of the compound microscope, employing 

 for the purpose an objective fitted with Lieberkiihns miiror and 

 adapted for opaque objects, since we can then see the most delicate 

 threads and the connection of one spot with ftnother. 



If we examine the specks more accurately, which is best done 

 with transmitted light in extremely thin horizontal slices of the 

 cuticle, we perceive that the threads of the fungus have on their 

 under side, exactly correspoudhig with each brown speck, an 

 irregular lobed process, by which it is firmly attached to the 

 epidermis (Figs. 2 & 4, b b). Those processes which are nearest 

 the tips of the threads of the Mycelium are frequently as colourless 

 as the threads themselves, but most of them have assumed a 

 brown tint with which a diseased state of the epidermal cells 

 with which they are iu contact is constantly combined. The con- 

 tents of these cells become brown and contract irregularly, while 

 the walls themselves acquire a similar tint which is deeper in those 

 which are lateral. This degeneration of tlie tissue, which at first 

 is confined to the cells in immediate contact with the processes, 

 seizes at a later period also the neighbouring cells to a greater or 



