VI. THE LEAF. 



(With special reference to evolution.) 

 1. Introduction. 



The leaf lias been dealt with in some detail under the headings of " Juvenile Leaf," 

 at Part LVI. and " Mature Leaf," at Part LVII. Although it is convenient to thus 

 differentiate between extreme forms of the leaf (and, indeed, of any organ), we must 

 remember that there are no hard-and-fast lines between the extreme physical (and, 

 indeed, chemical) characters of the leaves of any tree, much less of any species, but 

 insensible gradations. It would, indeed, require a cinematograph to show the complete 

 series morphologically. 



These intermediate forms have been recorded in this work, chiefly under 

 Descriptions of Species and Explanations of Plates, as the " Intermediate Leaf." So 

 far as I can recollect, I introduced the term, but I am afraid that it has been used more 

 or less loosely to indicate " A member of the series of Intermediate leaves." 



To some extent, though with less appropriateness, it would be proper to criticise 

 the term Juvenile Leaf and Mature Leaf in all cases in which it can be proved that the 

 ultimate Juvenile Leaf and the ultimate Mature Leaf respectively have not been referred 

 to. In other words, under the circumstances under which we obtain herbarium speci- 

 mens from the bush, leaves that we term Juvenile or Mature are such to the best of our 

 knowledge and belief at the time, and they may be deposed from their positions with 

 advancing knowledge. I have dwelt on the point elsewhere, and the matter is but 

 another illustration of the fact that morphological forms or characters are not absolute, 

 but are the concrete representation of the physiological combination of circumstances 

 that bring them about. In other words, they are an expression of the resultant of the 

 botanical forces concerned. 



This may be a convenient place to give a few hitherto unrecorded notes 

 concerning leaves. 



In describing E. Gunnii, Hook, f., says : " As is the case with other species of 

 this most difficult genus, no dependence can be placed on the size of any of the parts 

 or on the form of the leaves." (Lond. Journ. Bot., Ill, 499, 1844.) 



Considering a single character, we have an example of variation in the quality 

 (texture, colour, etc.) of the timber of an individual tree. Or, taking an instance from 

 the animal kingdom, wool of different qualities may be obtained according to its position ' 

 on the fleece. 



