THE CONICAL GROWTH OF TREES. 65 



tree is reawakened in the Spring of the next year, they no 

 longer grow, or assimilate formative material. They are 

 dead, rigid, unyielding. For the sap is drawn away from 

 these old and full-grown tissues, by the young and newly- 

 forming stratum of bark and wood, and although its flow 

 through the finer capillary vessels of the fibre-cells may 

 be again renewed, — this flow arises from causes purely me- 

 ehanieal, — there is no assimilation of formative material. 

 In fact, the only change that takes place in the fibre-cells 

 after the first year, is the gradual filling up of their cavi- ' 

 ties by deposits of lignine or earthy matter, whilst the duct- 

 cells, being devoid of sap, after the first year are never 

 filled up, as inspection plainly shows. 



Let the reader again refer to the diagram, which shows, 

 not only the conical growth of the primary axis of the branch, 

 but also the conical growths of its secondary and tertiary 

 axes, or branchlets and twigs, and how they are connected 

 with the primary axis. Commencing with the first, second, 

 or third ring from the outside, which form the foundation of 

 three successive conical deposits, and tracing them upward 

 over the summits of each branch and branchlet, he will find 

 that each forms a continuous and unbi-oken bed of woody 

 matter ; and he will easily understand, when the tree grows 

 again in spring (if we suppose the thick exterior and 

 bounding line of the diagram to represent the newly-form- 

 ing stratum of bark and wood-cells), how, from different 

 points of the surface newly-forming on the last year's 

 branches and branchlets, fresh shoots may be pushed 

 forth. It is thus, as the tree continues to grow, that a 

 series of new and more extensive communications are 

 annually opened with that grand reservoir of vegetable 

 food, the atmosphere ; and the newly-deposited living 

 stratum is just as continuous as that of former years, and 

 its life passes away with the falling of the leaves. For it is 

 the leaves which are the source of the formative material 

 which proceeds from them to the shoots, from the shoots to 

 the branchlets, and from th<| branchlets to the branches, 

 whose union forms the main stem of the tree, just as a 

 thousand little streamlets, descending from mountain and 



