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diluted with pure water. It is not difficult to convince oneself of 

 this, for the quantitj' of the virus employed is of great influence 

 upon the symptoms and the course of the spot-disease. If a consi- 

 derable quantity of virus is at once introduced into tlie plant, tho 

 first diseased leaves, which develop from the bud, not only show% 

 besides the usual symptoms, a remarkable relaxation and suspense 

 of growth, by which they remain much smaller than normal leaves, 

 but also deep, irregular pinnate or palmate incisions in the margin 

 in consequence of some lateral nerves remaining short. As the 

 chlorophyll-tissue thereby develops very imperfectly and as, especially 

 near the nerves, the formation of chlorophyll may be quite deficient, 

 these leaves get a peculiar striped appearance and by theii' shape 

 belong to the true monstrosities '). AVhen a small quantity of the 

 sap is used such deformations don't appear at all, so that it seems 

 to me that an increase in virulence of the sap under the said circum- 

 stances would not have escaped me. 



Consequently I consider it as certain that the virus can onlv be 

 reproduced in the manner described, with and through cell-multi- 

 plication of the plant. In my opinion this fact must be related to 

 the fluid or dissolved state of the virus, for, with regard, to a 

 contagium fixum, were its particles ever so small that they escaped 

 all m.icroscopic observation, there is no plausible reason why it 

 might not augment, like parasitical bacteria, out of the fosterplant. 

 It does not even appear impossible that a microscopically invisible, 

 but notwithstanding corpuscular contagium, might occasion visible 

 colonies on culture gelatine. A fluid virus, fit for diffusion like that 

 of the spot-disease, would penetrate into tiie gxdatine or the agar 

 and, if it were fit for reproduction, it would then alter the chemical 

 nature of the nutritive substances, which might perhaps be observed 

 by a change of colour or of refrangibility in the plates. When 

 „sowing" the virus on malt-extract gelatine, and on plates obtained 

 from some plant-infusion with 2"/^, cauesugar and 10''/o gelatine, — • 

 according to my experience excellent culture masses for t)acterja com- 

 monly occurring on plants, — such alterations could in no way be 

 observed. Moreover, though reproduction or growth of dissolved matter 

 is not quite inconceivable, yet, it is difficult to imagine in what way 

 such a process might be achieved. A division-process in the molecules 

 causing their multiplication, meets, to my mind, with great difhculties ; 

 even the conception of „molecules which take food", would seem to 

 me vague, if not inconsistent. The increase of the contagium now, is 



*) Oil one of my plauts sucli a leaf liiul taken the form of an ascidium. 



