214 Prof. H. Marshall Ward. The Relations between [Feb. 27, 



stances like glucose, acids, and soluble nitrogenous matters, the 

 protoplasm lining each cell is less capable of destroying substances 

 which can injure it — its respiratory processes being enfeebled — and, 

 in short, such a plant approaches the condition of a very young 

 seedling, or a plant growing in the dark. 



Experiments have proved that such plants not only offer less resist- 

 ance to the hypha of a parasite, but the very conditions which cause 

 the plant to abound in materials suitable to the fungus also suit the 

 f angus itself. 



Attention was then called to a peculiar parasitic disease, very 

 common in green-houses, gardens, &c, in this country and elsewhere, 

 and some cuttings of geraniums which had been wholly or partially 

 destroyed by it were exhibited. One curious fact is, that this fungus 

 causes a sort of rotten-ripeness of grapes on the Khine, and that these 

 mouldy grapes are those which are used to produce the finest wines 

 in some of the districts : the explanation is that the diseased grapes 

 undergo remarkable changes, by which the proportion of acid is 

 reduced, and the must of the grapes rendered richer. But although 

 in this case we utilise the effects of the disease -producing fungus, in 

 other cases these fungi cause epidemic diseases of clover, rape, hemp, 

 onions, hyacinths, and other plants. 



The symptoms and progress of these diseases were described, the 

 chief points being illustrated by lantern slides and actual specimens, 

 of which there was a collection on the tables. 



The fungus attacks the plant by destroying first its cell-walls, and 

 then its protoplasm, cell by cell: this it effects by excreting a series 

 of ferments or poisons. When it has destroyed the tissues, the 

 fungus proceeds to extend more rapidly, and the destruction quickly 

 advances. The fungus is as it were in the position of an attacking 

 army, its weapons being these soluble ferments, or poisons, capable of 

 dissolving the cell-walls and killing the living protoplasm in the 

 cells. 



The tissues of the host-plant, again, are in the position of a besieged 

 army ; the real fighting force being the protoplasm. The proto- 

 plasm is entrenched, so to speak, behind the cellulose cell- walls, and 

 it has in its interior stores or reserves of food-materials which may 

 be in a well replenished condition or the reverse. The hyphse of the 

 fungus overcome the cell- walls or out-works, by dissolving them by 

 means of soluble ferments, and it will be intelligible that the thick- 

 ness and solidity of these cell- walls are important in the matter ; 

 thin, soft, watery cell -walls being more easily penetrated. 



Once inside the walls, the fungus-hypha is face to face with the 

 real fighting contingent, however, the protoplasm ; and the fact was 

 insisted upon that circumstances affect the power of this protoplasm 

 to cope with the poison which the hyphas pour into it. So long as the 



