44 



LETTERS ON TREES. 



7. An extreme degree of this — natural, seemingly, 



to several sorts of trees, particularly the Beech, the 



Yew, the Thorn, and the Normandy Poplar — consists 



in sets of woody bundles (such as those connected 



with particular branches) grouping themselves toge- 



^ ^ ther year after 



Fig. 6.* 



year, to the ex- 

 clusion of other 

 bundles, and pass- 

 ing; down in masses 

 more or less dis- 

 tinct (Fig. 6). 

 The trunk has thus 

 given to it a colum- 

 nar or buttressed 

 aspect; and a sec- 

 tion of it, while exhibiting often great confusion in 

 the mutual relations of the zones and the cellular 

 tissue, shows, even more clearly than can be made out 

 from an inspection of the exterior of the trunk, both 

 the extent and the reality of the grouping. This 

 arrangement, you cannot fail to perceive, is in prin- 



tlieir branches and leaves fully exposed on one side, grow with com- 

 parative vigour, and form excellent timber on that side of the stem 

 where light and air are admitted ; while the latter, hemmed in on 

 all sides, are drawn up like bare poles, producing a small amount of 

 ill-conditioned wood." — Balfour's Class-Book of Botany, p. 428. 



^ Fig. 6, Section of stem of a tropical Climbing -tree, copied from 

 the English Encyclopcedia, art. Exogens. 



