1898] THE CHEMISTRY OE THE FOREST LEAF 183 



With reference to the scheme of the products of de-assimilation 

 exhibited on the right-hand side of the aforedrawn table, it may be 

 observed that a considerable experience in plant analysis is requisite 

 in order to appreciate it thoroughly. Suppose, for instance, that 

 we are determined to engage in a complete study of the chemistry 

 of the forest leaf, we must commence with the earliest growth of the 

 organ — in fact, we should commence with the winter buds, but at 

 any rate we examine the young leaves just unfolded, and we, by 

 appropriate methods of analysis, discover that one body seems 

 almost universally present in them all, and that body is a tannoid 

 compound (rutin or quercitrin). It is inevitably present because it 

 is the first formed product of the chlorophyll (i.e. the proteid) 

 substance that has spent its energy, and lies in the position of a 

 waste or excretum. But what then ensues ? 



The leaf progresses in growth. Oxidation more or less com- 

 plete supervenes on every item of its tissues and contents which is 

 not directly under the dominion of the reducing energy of the living 

 and vigorous protoplasm. The tannoid compound aforesaid is 

 gradually transformed more or less completely into volatile oil and 

 resin, or into tannin, but until the late autumn the change into the 

 latter body is probably never entirely and absolutely accomplished. 

 Practically in the majority of our forest trees there is no formation 

 of essential oil in the leaves, but there is always apparently a 

 residuary resinous body or a ' bitter principle ' extracted by benzene 

 or alcohol, and there is invariably tannin, the quantity of which 

 increases from spring till autumn, reaching its maximum about 

 October or November. According to Kraus, there is generally 

 twice as much in the October leaves as there is in the June leaves. 

 That some such progressive change ensues as is here described, even 

 supposing that a portion of the material formed is daily conducted 

 away into the bark and wood, there can be no doubt whatever. 



On the whole, therefore, it may be admitted as established that, 

 while the forest leaf is par excellence an organ of reduction so far as 

 its purely and distinctively protoplasmic energy is concerned, yet at 

 the same time very considerable and important oxidising processes 

 take place among the lifeless ruins, so to speak, of its spent and 

 exhausted activities. The bye-products, the waste of protein bodies 

 are only partially and slowly excreted and cast off, an expulsion 

 which dies gradually away in the old age and decrepitude of the 

 organ when autumn comes upon the scene, and the reducing agencies of 

 the protoplasm having been expended, the oxidising agencies of light 

 and air enjoy unrestricted sway crowned by the golden and crimson 

 glories of the autumn woodlands. P. Q. Keegan. 



1'atterdale, near Penrith, Westmoreland. 



