ORGANS OF NUTRITION'. 



155 



normal ramification of the tree, for the angle at which the 

 branch is given oif is frequently modified by a great number 

 of circumstances both natural and aitificial. His researches 

 have been almost confined to reticulated leaves, and he has 

 given the following table of plants in which the angles of 

 branching and A-enation were found to agree, — the angles 

 being taken immediately below the points where the branches 

 and veins were given oif: — 



Deg. 

 Beech 45 



Oak (large branches) 



" (small branches and "v 

 Cheny 



Portugal Laurel 

 Bav Laurel 

 Holly 



Rhododendron 

 Eose 



Laburnum (small branches) 

 Box, about 

 Thistle 



Thorn (lowest branches) 

 Ash ... 



Bird Cherry 

 Eed Dog- wood . 

 Alder 



Mountain Ash . 

 &c. &c. 



eins) 



65- 



50 



-70 



. 50 



.nO— 60 



50—60 



55—60 



. 60 



. 50 



. 60 



. 60 



60—70 



35—50 



. 60 



. 60 



. 45 



. 50 



. 45 



Dr. M-^Cosh also beheves "that the analogy between the 

 skeleton of the leaf, and the skeleton of the branch, may be 

 seen in a number of other points ; thus, some trees, such as the 

 Birch, the Elm, the Oak, the Holly, the Portugal and Bay 

 laurels, the Privet, the Box, will be found to send out side 

 branches along the axis from the root, or near the very root; 

 and the leaves of those trees have little or no petiole or leaf- 

 stalk, but begin to expand from nearly the very place where 

 the leaf springs from the stem. There are other trees, as the 

 common Sycamore (the Scotch Plane-tree), the Beech, the 

 Chestnut, the Pear, the Cherry, the Apple, which have a con- 

 siderably long unbranched trunk; and the leaA'es of these trees 

 will be found to have a pretty long leaf-stalk." The discussion 

 of these views further would be incompatible with our object; 

 and we refer those who desire further information upon these 

 points to Dr. M'^Cosh's papers read before the Botanical Soci- 

 ety of Edinburgh, and his works on the subject. 



Composition. — Leaves are divided into simple and compound. 

 Thus a leaf is called simple if it has only one blade (figs. 288 — 



