300 EVERGREENS. 



If the experiment is made after the young 

 leaves are expanded, but before the old ones show 

 any discolouration or other symptom of decay, and 

 made when the sun shines brightly, the contrast 

 is very striking ; so much so, that an instrument 

 is quite unnecessary ; for the young leaf feels cold, 

 and the old one warm. This shows that all ac- 

 tion in the old leaf has ceased ; because it is the 

 action, the evaporation of moisture at the surface 

 of the leaf, which preserves its coolness. 



In all cases where there is an annual leaf, there 

 is also an annual plant. In 'trees which last for 

 years that is a very beautiful study ; and if we 

 could separate the oak which has stood a century 

 into the hundred oaks that have been produced in 

 the successive years of that century, there is 

 nothing in the museums half so curious. But we 

 can trace them in the cross section of the bole, 

 and so virtually arrive at all the rest. When the 

 infant oak sprouts out of the acorn, it is nothing 

 but pith and pellicle, the former a small portion 

 of jelly, and the latter very soft and tender. Even 

 then the oak is an organized being, from the mo- 

 ment that we can discern it; and, previous to that, 

 there is nothing but conjecture. The vital prin- 

 ciple of the plant is not a quality or property of 

 the pith, or of the pellicle, for both of these are 

 mere matter, and neither of them could of itself 

 originate an oak any more than the soil in which 

 the acorn is set. The life consists in the union of 

 the two, the action of the one upon the other ; 

 and that action takes place at the surface where 

 they meet. During the first year that action con- 

 verts the food of the plant (derived at the first 

 from the cotyledons, or lobes of the acorn, and 

 then from the soil and the air) into a new sub- 



