90 PBOPAGATIOK OF PLANTS. 



trated, and its organizing power increased. This is the 

 simple fact which lies at the foundation of all those phe- 

 nomena which are brought forward to support the 

 groundless hypothesis of a decending bark sap." In 

 another place he says : " When an Apricot graft grows 

 from the trunk of a Plum tree the latter is naturally and 

 by degrees clothed with Apricot wood, for out of the same 

 soil an Apricot tree would merely take up the same crude 

 material as the Plum tree," etc. But those who oppose 

 this idea of a downward flow of organizable sap in the 

 liber appear to have overlooked the individuality of the 

 functions of the cells, and the fact that while one set or 

 group may be secreting one kind of substance, or per- 

 forming certain functions, another group may be doing 

 something quite different, as I have already explained 

 elsewhere. 



Practical propagators of plants know that the cells of 

 the stock and those of the cion always remain distinct 

 in each, preserving their individual type, and even the 

 old and excretory bark enclosing them retaining its pecu- 

 liar original characteristic. Peaxs grafted on Quince roots 

 never change the latter into the former, and we may 

 build up a tree of alternate sections of Pear, Quince, 

 Thorn and Medlar, and each section or part of the stem 

 wUl retain its individuality, although the roots may be 

 of one species and the branches and leaves of another. 

 The cells of each take from the passing crude sap, or 

 descending organizable matter, the materials needed to 

 build up and retain their own individual structure. 



If there were no descending organizable sap in the 

 liber or inner bark, then the girdling of trises would have 

 no more than a temporary effect upon growth ; but the 

 pioneers in our American forests have proved to us ihat 

 to remove a ring of bark and the mere severing of the 

 outer layer of alburnum wUl cause the death of any kind 

 of tree within a twelvemonth. By this simple process 



