THE SPREAD OF PLANT DISEASES. 1 L9 



satioii. Or, finally, perhaps the chief trouble was in the use of 

 Avater. The management of water in hothouses is a fine art. 

 Nothing requires better judgment and in nothing is our friend 

 less experienced. The plants suffered at times and in particular 

 parts of the house, let us say, from lack of water, and then were 

 drenched by the hired man ; or the unsatisfied owner, seeing that 

 things were going wrong, took the watering out of the hands of 

 the foreman and daily flooded the house himself according to 

 ideas evolved out of his own inner consciousness. About this 

 time slugs, scale insects, red spider, plant lice, nematodes, and a 

 variety of fungous diseases made their appearance in alarming 

 proportions, and some man of my profession was sent for. Of 

 course, he found a most interesting set of conditions, — interest- 

 ing, I mean, to the pathologist, — and, possibly, was able to afford 

 the disheartened grower the cold comfort of some good advice 

 about what not to do next time. This is an extreme case, and 

 yet there are plenty of such cases every year around every great 

 city, and the troubles and failures are not all confined to begin- 

 ners or to plants grown in hothouses. If the tyros were the only 

 sufferers, we might be content to let them alone, trusting to the 

 hard doctrine of the survival of the fittest as the all-sutficient 

 remedy. This, however, is not the case, even old growers some- 

 times experiencing great losses which might have been avoided. 

 There are now so many people engaged in growing things for 

 market, and competition on most crops is so very close and the 

 profits so small, that even the most experienced and successful 

 grower must stop every leak in his expense account, and take ad- 

 vantage of every least chance for increasing the quantity, quality, 

 earliness, etc., of his crops. This he can do only by a thorough 

 understanding of all the conditions necessary for successful 

 growth, the avoidance of parasitic diseases being one very im- 

 portant consideration. It is just here that plant physiologists 

 and pathologists, while themselves learning much from the prac- 

 tical grower, may nevertheless be able to render him very material 

 assistance. As such an individual, I have been invited to ad- 

 dress you. 



If, however, you expect me to tell you today how parasitic dis- 

 eases may always be avoided, you are expecting the impossible 

 and will be disappointed. The most I can do is to tell you how 

 some of them may be prevented, and put you on your guard as to 



