1706 



ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



(not pear blight) causes defoliation of 

 the pear trees during the early part of 

 the summer, the fruit buds which have 

 set are caused to come out and a full 

 bloom in the early fall is the result. The 

 attack of the fungus on the leaves causes 

 a premature setting or development of 

 the buds. As climatic conditions follow- 

 ing this period are normal to the tree's 

 growth, of course, these newly formed 

 perfect buds will push. But we do not 

 need to go so far as the pear leaf blight 

 of the pear tree for an example. We 

 have even noticed here in this district 

 that trees having their foliage badly in- 

 jured by insect agencies will also tend 

 to make a late secondary growth. But 

 you will say, "What does all this have 

 to do with understanding the cause of 

 the secondary sprouting of the potato?" 



Under our climatic conditions during 

 midsummer all plants transpire very 

 freely; that is to say, they lose water 

 by evaporation through the stomata or 

 breathing pores very rapidly. The higher 

 the temperature and the lower the rela- 

 tive humidity of the atmosphere the 

 greater the rate of transpiration. At 

 very high temperature, say from 90 de- 

 grees to 110 degrees, with the relative 

 humidity of the atmosphere 10 to 15 per 

 cent, the rate of transpiration is so great 

 that the roots of the plant cannot take 

 water fast enough from the soil to supply 



the demand made by the foliage. When 

 this point is reached, injury to the whole 

 plant is the result and there is a ten- 

 dency to check the growth of the tubers 

 and cause the buds to set prematurely. 



It must be remembered that the tuber 

 of the potato is an enlarged underground 

 stem, and the eyes of the tuber are just 

 as truly buds as the axillary and terminal 

 buds we find on the stem above the 

 ground. Now, as soon as normal cli- 

 matic conditions return, there will be a 

 tendency on the part of the entire plant 

 to resume growth, and the buds on the 

 tuber will tend to push jilst the same as 

 those on the stem, the result being that 

 both secondary tubers and shoots on the 

 stems will be formed. Under severe con- 

 ditions it will make little difference 

 whether the plants are well supplied with 

 water or not. It has been noted that 

 this secondary sprouting has taken place 

 even where the potatoes had been well 

 irrigated and where the soil contained 

 a sufficient supply of water. The reason 

 for injury, even where water was sup- 

 plied artificially, is that the root system, 

 even under the best conditions, could 

 not supply the demand for water made 

 by the leaves. 



Since the water stream going upward 

 from the roots through the stem follows 

 the fibro-vascular bundles, it is easily 

 seen that if the injury to the part of the 



White Wonder. 



Peach Blow. 



Mammoth Pearl. 



