440 BOAKl) OF AGRICULTURE. [Pub. Doc. 



develoi)ment of fungi. The most perfect and the hardiest 

 plant organism can become diseased in a remarkably short 

 period of time, if the conditions that are suitable for its nor- 

 mal re<|uirements are changed. For example, the geranium 

 constitutes one of our most hardy greenhouse plants, never- 

 theless, if such a rugged plant is placed under a bell glass, it 

 becomes sickly in a very short thne, and in a few days it 

 will succumb to disease, even when subject to light and sup- 

 plied with all of the necessary elements of plant food. Such 

 an experiment is interesting, as showing how (juickly the 

 healthiest organism can fall a prey to disease and become 

 dilapidated. 



The explanation of the ai)pearance of some of our most 

 troublesome diseases affecting plants at the present time can 

 be found in })art in the practice of increased forcing, and is 

 also due to the fact that new parasitic organisms have been 

 introduced from time to time from other countries through 

 traffic. Some of these fungi, however, Avhich have recently 

 proven disastrous, have been with us for some years, if not 

 always ; and the reason of their becoming more troublesome 

 at the i)resent time can be attributed to the increased pro- 

 duction of more succulent, tender plants, brought about by 

 forcing, which enables these parasites to find more favorable 

 conditions in which to thrive. With every modification and 

 innovation in the growing of plants there are likely to occur 

 new difficulties and obstacles to overcome. 



Constitutional weaknesses, which dcveloj) in some varieties 

 and are inherited in others, are unfavorable to immunity. 

 Varieties of carnations inclined to succulency, or containing 

 two or three per cent more water content in their leaves, 

 have proven much more susce})tible to rust than those con- 

 taining less water. 



There is little doubt but that many diseases could be pre- 

 vented by modifications in the methods of growing plants, 

 if such could be adopted. The so-called " drop" in lettuce 

 would prove less disastrous if the })lants could be elevated 

 from the soil suffici(>ntly to allow air and light to penetrate 

 to the stem. This would result in producing firmer and 

 more resistant tissues, 



