Summer Meeting. 93 



abnormally shortened. The danger from this class is likely to be under- 

 estimated because we do not see the rapid injury to the plant, but it is 

 none the less real. 



In contrast to these fungi, which exert a destructive influence upon 

 their hosts, there are others which seem to conserve the life of their host 

 plant. This phenomenon is particularly conspicuous among the rusts. 

 These, throughout their whole development, adapt themselves to an 

 existence with living host cells, so that the latter die only after the repro- 

 duction of the fungus. 



DISPOSITION OF PLANTS TO DISEASE. 



As all practical horticulturists know that certain varieties of fruits are 

 more susceptible to fungous disease than others, this inherent disposi- 

 tion is but little understood as yet. 



There is an accidental disposition to disease which is better under- 

 stood. It depends largely upon the nature of the epidermis inclosing the 

 plant organs. The stems of many plants are protected from intruding 

 fungi by a corky layer of epidermis, and still better after they have pro- 

 duced a layer of bark. This explains why they need to be protected by 

 frequent spraying in early spring. It explains why the "damping off" 

 fungi only attack seedlings so long as they are unprotected by a corky 

 epidermis. This is also exemplified by the fact. that thin-skinned fruit 

 are more liable to decay than thick-skinned ones. 



Plant organs, rich in water, are in a condition which disposes them 

 to attack much more than drier parts. Prolonged wetting of a leaf from 

 rain favors germination of spores, and at the same time, by softening the 

 leaf, facilitates penetration of the germ tubes. 



A plant may be said to be in a condition of abnormal disposition to 

 disease when deprived of its natural protection. This is the case with 

 trees which have received wounds such as those inflicted by hailstones or 

 the boring of insects. 



Defective nutrition is another condition which is favorable for the 

 entrance of fungous diseases. The cells of a poorly nourished plant are 

 not in a vigorous condition and can not resist the penetration of fungi. 

 It has been found that the rust on cotton may be greatly diminished by 

 the application of land plaster and salt. 



HOW MAY THE HORTICULTURIST COMBAT THESE FUNGOUS DISEASES? 



Measures are known for the prevention and cure of many fungous 

 diseases. These have been deduced from the biology of the parasite and 

 its relation to its host. 



