140 Animal Morphology. 



their leaves till very late in the season, as the blackberry 

 and the privet trees, or shrubs, than in those trees which 

 shed their leaves in mid, or late in the autumn as, say, in 

 September and October in this country ; but to this general 

 statement there are many exceptions. 



2nd : The density of wood, especially in its centre, when 

 a tree is in its vigour say, 40 to 60 years of age and the 

 bark in the trunk is complete, is, cczteris paribus, harder wood, 

 especially in its centre, in ratio to the thinness of the mid-rib, 

 as compared with aggregate of the transverse ribs (or lateral 

 nerves). To illustrate this matter, a cherry tree in its 

 centre is rarely ever hard wood when cut at 60 years 

 of growth, though the intermediate wood is hard ; the 

 same maybe said of the horse-chesnut. If, then, any of these 

 trunks are compared with the beech or the oak at their 

 centres, at 60 or 80 years of growth, the hardness is much 

 greater in the latter than in the former. Then take an oak 

 leaf and a beech-tree leaf, and examine the transverse ribs 

 with the mid-rib, and the mid-rib is scarcely equal in the 

 amount of its substance as compared with the transverse ribs; 

 but in the cherry tree, and especially in the chesnut tree, 

 the mid-rib is very large as compared with the transverse 

 nerves. 



Again, the size and length of the nerves to the mid-rib 

 of the leaf, appears to have something to do with 

 the length of the woody fibre, or with the fragibility 

 of the trunk or larger branches. This is well illustrated 

 by two trees which develop timber in moderately equal 

 ratios of time namely, the beech and the elm ; the beech 

 forming timber in many localities where the other grows- 

 well, but the beech makes timber the quicker of the two. 

 The beech leaf is much larger and longer altogether than 

 the elm, and its timber is far less brittle, from the woody 

 fibre being longer than that of the elm. 



