434 Prof. H. Marshall Ward. The Relations between 



1 I 



Fig. 12. Spores of JBotrytis germinating on the epidermis of a snowdrop, and 

 infecting it by means of their germinal tubes, the tips of which penetrate the 

 cell-walls by means of secreted zymases, and cause them to turn brown at the 

 points of entrance, as shown by the shading. (Highly magnified.) 



everything which promotes or retards the vigour of the mycelium. 1 

 regard the conidium as distinct from any vegetative piece of mycelium 

 chiefly in its capacity to form the necessary (cellulose-dissolving, &c.) 

 ferment or zymase* in greater quantity or in a shorter time (with 

 respect to the size of the organ), and look upon its size, shape, and 

 colour, &c, as so many adaptations to the mode of life of the 

 fungus. 



Be this as it may, the conidia vary in infective power according 

 to their nutrition — i.e., according to the substratum on which the 

 mycelium grows — and according to the generation to which the coni- 

 dium belongs, i.e. (as I interpret it), according to the increasing 

 vigour of the successive mycelia which produce the conidia.f 



This latter fact is best demonstrated as follows : A crop of conidia 

 is grown on a given pabulum, e.g., on the moist sclerotium ; the conidia 

 are sown on the cut surface of ripe, sweet pears, and produce mycelia, 



* See ' AnnaL of Botany,' yol. 2, 1888, p. 356. 



f Kissling (op. cit., p. 31) has proved this for Botrytis cinerea. 



