JOURNAL 
The New York Botanical Garden 
Vou. i, “November 1902. ne No. 35. 35. 
HEALTH AND DISEASE IN PLANTS.* 
A plant is in health when all of its organs or parts are doing 
their proper work, and the processes of growth and reproduction 
are going forward in the natural and regular manner. dis- 
eased condition results when for any reason an organ fails to 
thus perform its usual normal function. The causes that induce 
disease are very numerous and are often obscure. For con- 
venience diseases may be grouped under three headings: (1) 
environmental, (2) functional pe (3) parasitic, 
nder environmental diseases are classed those disturbances 
of normal growth caused by uncongenial surroundings, such as 
unfavorable soil conditions, too much or too little water, the 
absence or over-abundance of some of the food elements, or 
unsuitable soil temperatures ; unfavorable atmospheric conditions 
caused by the pollution of the air with smoke or gases; or 
unfavorable position as to sunlight. Such unfavorable surround- 
ings often cause a slow and feeble, through perfectly normal, 
growth that should not be confused with disease. It is starvation 
or semi-starvation and not sickness. The so-called “ scalding” 
of plants after unusually heavy and protracted rains, the “tip 
burn” of lettuce and potatoes due to exposure to bright sun- 
shine and dry winds after periods of wet cloudy weather, and the 
chlorosis or yellowing of the foliage of fruit trees on alkali soils 
in the West may be mentioned as examples of this class of 
diseases. 
* Lect g in the Aut t the Museum, New York Botanical Garden, 
September 11, 1902. 
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