120 DEVELOPMENT OF COMPOUND 



then the same general laws which govern the development 

 of the branch and its ramifications give form to its leaves, 

 which exhibit in their midrib and its ramifications through 

 the parenchyma of the blade, a miniature copy of the branch 

 itself 



^c is undeniable chat this theory of Dr. McCosh has been 

 received with coldness and distrust by scientific men, although 

 Professor Balfour, of Edinburg, has very properly given it a 

 notice in his " Class Book of Botany," but without commit- 

 ting himself as to its general soundness. In science it is not 

 permitted to yield to imagination. If we would give currency 

 to new truths, and obtain their endorsement as such by men 

 filling a high and responsible public position, it must be seen 

 that we have been guided solely by well-known and estab- 

 lished facts in their development. There must be a stern 

 determination to give a true and faithful portraiture of Nature 

 and her operations, which, the more they are studied, the 

 more they delight us by their grandeur and simplicity. 



But do we interpret Nature correctly when we say that 

 the leaf is nothing but an expansion of the fibre and paren- 

 chyma of the branch, that the ramifications of its fibrous 

 portion or skeleton follow the same general laws as branch 

 ramifications, that the leaf and branch are, in fact, homo- 

 typal ? 



Of course it is understood that these general laws of stem 

 or branch ramification are somewhat modified in the leaf. 

 Thus in every tree there is a certain normal angle at which 

 branches are given off from the stem, and this angle varies in 

 different trees. For instance, in the Norway Spruce Fir 

 (Abies excelsa) the branches are drooping or pendulous, in 

 the Hemlock Spruce (Abies Canadensis) they grow out hori- 

 zontally from the stem, and in the Lombardy Poplar (Populus 

 dilatata) their growth is almost vertical. Moreover, the angle 

 which the branches make with the stem varies even in the 

 same individual tree, for it not only increases with the age 

 of the branch, but it is greatly modified by the position of 

 the branches and the influence of surrounding agents. As a 

 general rule, the lower branches of a tree grow more horizon- 



