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the fiftieth part of an inch in length, while the little spores or re-productive part will 

 be about the two-thousandeth part of an inch. It is exceedingly minute. Now, let us 

 follow the history further. These drop, after they have reached the mature condition. 

 One is generally called a Conidium while many are called Oonidia. After it has fallen on 

 a leaf or some other part of a plant, if the conditions are favourable it will pursue 

 further development; but if the conditions are not there it will get no further. 

 Now, what are the conditions? For this genus, in the fungi, they are moisture and 

 warmth. It wants a good deal of moistui'e. If there is no water present the spore 

 is not going to be able to develop. It is not merely a little moisture, but something 

 that these spores can float in. After it has rested awhile it begins to divide up, as 

 you see in the drawing. Shortly after that these break out of this sort of structure 

 and assume that form — a little rounded body with a couple of tails. Then this 

 rounded body begins to move ; the hair-like structures help it to move about, and if 

 there is no watei- present that is not sufficient moisture to work in, it can go no 

 further in its development. So you see how necessary it is for this form to have 

 moisture and warm temperature. If the conditions are favourable and they are able 

 to spin about, these little spores, technically called Zoospores, drop their tails and 

 assume that form. Then it throws ou't a sort of tube, and you have the whole thing 

 starting into growth. If it is upon the leaf or fruit, or any part, it will grow and 

 develop into the plant we have already seen. But here is something peculiar — we 

 notice there are no less than three ways in which this Conidium can develop. One 

 way I have described, and the second way is represented here, where the whole of 

 the contents pushes out and commences to develop in the way you see in these two 

 figures. It does not break up into five or six parts, but it comes out and assumes 

 this form and developes. Another form is where the whole of the protoplasm, the 

 whole of the matter in the Conidium, comes out into the form of a tube and permeates 

 the tissue of the plant, and repeats the life history of the fungus, as I have already 

 described. So, from a Conidium you have three diflE'erent ways in which it may 

 develop itself: but the most common way is the one that I have described some- 

 what minutely at the beginning. Now is that all ? That explains the development 

 of it through the growing season, and that form of development is very rapid, so 

 that the fungus soon spreads [over a very large area. But there is another form of 

 development. In among the tissues of the plant you will find some of the rounded 

 bodies such as you see there. I do not like to mention the technical names, yet it 

 seems to be almost necessary and not out of the way before intelligent men. It is here 

 called Oogonium and the other organ Antherridium. The protoplasm of the one 

 mingles with that of the other and you have a germ cell produced — another form of 

 reproduction altogether. 



The form I described at first when referring to spores is termed a sexual and 

 what I have described now the sexual. This latter form carries the plant into an- 

 other year : the other is a form for rapid propagation. Here is a section and these 

 little black spots are the Oospores, or germ cells, prepared for growth next spring 

 or summer. So much for the life history of the Peronospora viticola. Now, the 

 question of greatest importance to you is how to fight against it. I cannot help but 

 think there is a great deal of interest in knowing the life history of these parasites. 

 It is very well to know how to kill it, but when a person knows all the outs and ins 

 of the complicated history of these obscure forms of life it gives an interest to his 

 labour which he otherwise could not possess. How are we going to battle against it? 

 Many remedies have been tried and some of them have been successful. This fun- 

 gus is in the tissues of the plant, so that you are not very well able to get at it. 

 Consequently, whatever course you may pursue, it must be along the line of preven- 

 tion rather than cure. You must prevent it rather than fight it when it has got 

 there. On general principles the remedj' for all these things is to have the plant 

 vigourous. Vigour in a plant, as in the animal and in the human being, has a wonder- 

 ful power to resist the attacks of disease of any kind. So on general principles we 

 always speak of trying to have the plant as vigorous as possible. It has been found 

 that lime has a very destructive effect. So if you have a solution of lime — of hydrate 



