70 POMOLOGY 



similar to "ringing" takes place with its attendant results as 

 discussed previously; i. e., disease such as canker, or forms 

 of winter-injuiy, damage by rodents or borers, or mechanical 

 injuries, may interfere with the flow of the sap through the 

 tissues of the tree. Just what disturbance occurs in the 

 reserves of the tree might have to be determined for any 

 given case, but it would be explained on the basis of nutrition 

 entirely. 



66. Light. — That a close relationship obtains between 

 the amount of light available and the production of fruit- 

 buds must be patent after a consideration of the foregoing 

 paragraphs. Throughout this discussion it has been pointed 

 out from various angles that the amount of elaborated food 

 materials within the plant together with their quantitative 

 relation (and probably a qualitative) to one another consti- 

 tutes the crux of the entire problem. Since the synthesis of 

 many of the plant products is dependent on light as a source 

 of energy, it is apparent that neither vegetative extension 

 nor the differentiation of flowering parts could proceed 

 without a proper amount of light. Just what intensity and 

 duration of light is necessaiy for the maximum production of 

 flower parts is not now known. In general, it requires a 

 greater light intensity for flower-bud formation than for 

 vegetative development. This is seen in the comparative 

 lack of flowering in the interior of dense unpruned trees. 

 Not only is fruit-bud formation partially suppressed under 

 these conditions, but the growth is weakly vegetative and 

 if the shading continues the spurs and branches die. 



In Plate I is shown the effect of shading a peach tree with 

 a light-weight cotton cloth. The twig to the left was taken 

 from an adjacent unshaded tree of the same variety. It 

 will be noted that there is a suppression of branching in the 

 shaded tree and usually only one leaf occurs at a node. This 

 modification in growth necessarily lessens the number of 



