215 



condition has gone too far the plants may recover with the access 

 of sufficient light, but, owing to their abnormally thin and watery 

 tissues, they are particularly liable to be killed or damaged by 

 frost, fungi, and other injurious influences. 



191. Somewhat similar to etiola- EEect ? f 

 tion is the condition produced by an excess of moisture 



in a plant. This is chiefly due to transpiration not being 

 sufficiently active to deal with the quantity of water 

 pumped into the plant by the roots. The tissues become 

 over-saturated with water, food materials are excessively 

 diluted and can only be transported in sufficient quantity 

 very slowly from one part of the plant to another, in conse- 

 quence of which, as in the case of etiolation, growth in 

 length is considerable, but the watery tissues are not properly 

 matured and are very liable to be damaged by fungi, insects, 

 frost, etc. This condition is, of course, distinguished from 

 etiolation by the fact that green chlorophyll is present in the 

 leaves and that the disease occurs in plants which have access 

 to light. Plants with an abundance of water available for 

 their roots, which are growing in a saturated atmosphere, are 

 liable to suffer from the condition here described. 



192. Winds, besides uprooting Effect of 



trees, breaking their stems and branches and causing the ' 

 development of stunted and misshapen crowns usually 

 bending away from the prevailing wind direction, 

 impoverish the soil by dispersing dead leaves and debris, 



thus preventing the accumulation of humus and also diminish 

 the available supply of moisture in the soil. Winds may be 

 also exceedingly destructive to plants by increasing transpira- 

 tion. Dry winds in cold frosty weather are particularly 

 injurious, the roots in the cold soil being then unable to replace 

 the water removed by transpiration, the plants being more or 

 less injured, if not killed, by desiccation. 



Observations have shown that the velocity of a wind which, 

 at a height of Ij feet above the ground, was only 22 '2 miles 

 per hour, may be as great as 42*7 miles per hour, at a height of 51 

 feet above the ground. Consequently tall plants and especially 

 tree -growth suffer much more from winds than shrubby or 

 herbaceous growth. It should be noted that in the case of the 

 Banana the tearing of the large leaves by the wind is a normal 

 condition leading to advantageous aeration of. the leaves. 

 Winds are also advantageous in the way of distributing pollen 

 and seeds and aiding the distribution of plants. 



