334 HORTICULTURE, FORESTRY, FLORICULTURE 



elaborated in the leaves, just as the leaves need the water sent up 

 from the roots. Hence the interdependence of root system and 

 crown, which must be kept in proportion when transplanting. At 

 least, the root system must be sufficient to supply the needs of the 

 crown. 



Sap Up and Sap Down. The growing tree, in all its parts, is 

 more or less saturated with water, and as the leaves, under the in- 

 fluence of sun and wind and atmospheric conditions generally trans- 

 pire, new supplies are taken in through the roots and conveyed to 

 the crown. This movement takes place even in winter, in a slight 

 degree, to supply the loss of water by evaporation from the branches. 

 In the growing season it is so active as to become noticeable ; hence 

 the saying that the sap is "up," or "rising," and when, toward the 

 end of the season, the movement becomes less, the sap is said to be 

 "down." But this movement of water is always upward; hence the 

 notion that there is a stream upward at one season and in one part 

 of the tree, and a stream downward at another season and perhaps in 

 another part of the tree, is erroneous. The downward movement is 

 of food materials, and the two movements of water upward and food 

 downward take place simultaneously, and depend, in part at least, 

 one upon the other, the food being carried to the young parts, wher- 

 ever required, by a process of diffusion from cell to cell known as 

 "osmosis." 



These food materials are, by the life processes of the active 

 cells, changed in chemical composition as need be, from sugar, 

 which is soluble, into starch, which is insoluble, and back into 

 sugar, and combined with nitrogenous substances to make the cell- 

 forming material protoplasm. 



In the fall, when the leaves cease to elaborate food, both the 

 upward and the downward movement, more or less simultaneously, 

 come to rest (the surplus of food materials, as starch, and sometimes 

 as sugar, being stored for the winter in certain cell tissues), to begin 

 again simultaneously when in spring the temperature i$ high 

 enough to reawaken activity, when the stored food of last year is 

 dissolved and started on its voyage. The exax;t manner in which 

 this movement of water upward and food materials downward takes 

 place, and the forces at work, are not yet fully understood, nor is 

 there absolute certainty as to the parts of the tree in which the move- 

 ment takes place. It appears, however, that while all the so-called 

 "sapwood" is capable of conducting water (the heartwood is prob- 

 ably not), the most active movement of both water and food mate- 

 rials takes place in the cambium (the growing cells immediately 

 beneath the bark) and youngest parts of the bark. 



The deductions from these processes important to the planter 

 are : That injury to the living bark or bast means injury to growth, 

 if not destruction to life ; that during the period of vegetation trans- 

 planting can be done only with great caution; that the best time. to 

 move trees is in the fall, when the leaves have dropped and the 

 movement of water and food materials has mostly ceased, or in 

 spring, before the movement begins again, the winter being objec- 



