44 INTRODUCTORY. 



state, accorfling to season, is a layer of organizable material, 

 called canibiuin, which may be regarded as the seat of life of 

 the plant." 



" Investigation seems to demonstrate that the cambium 

 layer is the seat of life, and that whenever the direct commu- 

 nication between the root and the foliage is cut off in this 

 layer during one entire season of growth, the whole plant per- 

 ishes. It has also been determined l>y experiment tliat if sev- 

 eral rings of bark be removed from a growing shoot in such a 

 manner that on one of the isolated sections of bark there be no 

 leaf, while leaves remain on others aljove and l)elow this, then 

 the leafless section will fail to make any growth in any part. 

 All other sections, if furnished with one or more healthy leaves, 

 will increase in thickness by the forination of new leaves, of 

 Avood and bark. This seems to prove that the material for 

 growth is elaborated by the leaves, and is transmitted only 

 through the cambium, and has no power of j)cnctrating the 

 tissues of the wood." 



" The ])eculiar vital and organic power of the caml)ium is 

 remarkably illustrated in the structure and grf)wth of grafted 

 trees. Every person is aware that pear trees are grown upon 

 quince roots, and that they often ])ear finer fruit than when 

 cultivated as standards. This is doulttless oAving to the fact 

 that quince roots, being diminutive, furnish less water to the 

 leaves, which thus elaborate a richer sap, and ]U'oduce more 

 perfectly developed wood and fruit." 



"The apricot may 1)e grafted on the jtlum, and tlic peach on 

 the apricot, and the almond on the peach ; and thus we may 

 produce a tree with plum roots and almond leaves. Tlu- 

 Avood, hoAA^ever, of the stem Avill consist of four distinct varie- 

 ties, though formed from one continuous cambium layer. 

 BeloAv the almond Avood and bark avc shall have ])erfect i)each 

 Avood and bark, then perfect apricot Avood and bark, and at 

 the bottom perfect plum AVood and l)ark. In this curious 

 instance Ave see the intimate corres|)on(lence Ix'tAvi-en tlie bark 

 and the leaf; for if Ave should remove the almond l)ranches 

 we might cause the several sorts of Avood to develop buds and 

 leafy tAvigs, each of its oAvn kind. Each section of the com- 

 pound stem has its seat of life in the cambium, and the cam- 

 bium of each re])roduces cells of its oAvn sjiecies out of a 

 common nutrient fluid. Thus there is seen to be a floA-f of 

 sap U})Avard in the AVOod, and a floAV of organizal)le material, 

 essential to the life of the plant, ]»roceeding from the leaf t(^ 

 the root, through the bark and the cambiinn layer. From 

 this perfected sap the groAvth of the season is formed, and 

 provision for the beginning of the next season's groAvtb is also 

 stored u]), commonly in the root." 



