ME. BEEKELEY ON THE POTATO MUEEAIN. It 



perfect, they have always been superficial and partially greened 

 by exposure to light. 



The disease, however, is in general subsequent to the decay of 

 the haulm. Now, even granting that no visible mj'celium is 

 present in the decayed spots when first exhibited, I cannot grant, 

 taking the ascertained facts into account, that they are inde- 

 pendent of the fungi. For without having recourse to the notion 

 of the juices of the plant in general being vitiated by the fungi on 

 the leaves which, indeed, is not consistent with the case just men- 

 tioned as brought forward by Decaisne, and if it were, leads at once 

 to the question of the production of the fungus from diseased mat- 

 ter without pre-existent germs, it seems to me most certain, from 

 observation of those fungi which grow from the tissues of plants, 

 that minute particles, too small to be distinguished by the 

 highest powers of the microscope, must be carried about with 

 the juices, and when fitting circumstances concur, proceed to act 

 upon the tissue with which they are in contact.* That under 

 certain circumstances foreign particles should produce disturb- 

 ance of the system is not more surprising than that a moment's 

 breathing an infected atmosphere or the least particle of virus 

 taken up by the absorbents in the human frame should produce 

 such extensive mischief, while in other cases constant exposure 

 to the malaria and more thorough inoculation prove absolutely 

 harmless. That the mould in the tubers should commence by 

 producing decay, contrary to its presumed habits in the foliage, 

 is not so curious as that under such anomalous circumstances 

 the mould should be produced at all. I can see, on mature 

 reflection and consideration of all the diflficvdties of the case as 

 far as they occur to me, nothing at all absurd in Dr. Morren's 

 views, in which if there be difficulties not solvable at present, 

 there are at least as great difficulties on the other side. 



A somewhat analogous decay is now attacking Swedish tur- 

 nips, commencing in little sinuous lines, which follow the course 

 of the scalariform vessels, around which dark granules are de- 

 posited somewhat after the fashion of those in the potato cells. 

 It is curious that in extensive fields the foliage is to a very great 

 extent destroyed by Botrytis parasitica, a nearly allied species. 



* It is well known that bunt is communicable by rubbing sound grain with 

 the spores of the fungus. It does not seem to have been ascertained at 

 present how the spores act : whether they vegetate on the surface, and send 

 their mycelium into the tissue of the young plant, or whether the contents of 

 the spores are imbibed. The usual mode of gei-mination in fungi is a pro- 

 trusion of the membrane of the spore ; but it is very pi'obaljle tliat the minute 

 contents of the spore or its protruded shoot, when absorbed and circulating 

 with tlie juices, would produce the perfect fungus under favourable circum- 

 stances. The spores themselves could not enter the stomata. 



