2 
184 The Vegetable Individual in its relation to Species. 
the paradoxical words of Schleiden:* ‘ No tree has leaves.” ~ 
The leaves, in fact, never grow out of the woody portions of the 
tree, but only on its herbaceous extremities, which grow upon 
ation. 'T'hiscommon ground, namely the woody stem, which is 
almost lifeless in comparison with the herbaceous parts engaged 
in active growth, is annually covered with a vigorous sheath un- 
der the protecting bark, and this sheath is the ground of the nour- 
ishment of all the vegetating herbaceous extremities. This 
sheath is the so-called cambium, a layer of active, living tissue 
which, contemporaneously with the lignification of the herba- 
ered in its turn in the following period of vegetation with a new 
layer, which, again, will be the immediate supporter of the new 
generations. ‘The history of the grand development of nature 
on the surface of our globe presents an analogy which may per- 
haps serve to set this relation in a clearer light. The successive 
geological formations superposed during the course of countless 
ages, present, buried in their depths, the traces of as many forma- 
tions of the organic world, each of which carpeted the then st- 
perior stratum of the earth with a new life, until it found its own 
grave in the succeeding formation, when a new uprising of or- 
anic life took its place. In the same way the stem of a tree is 
a multistratified ground, in whose layers the history of earlier 
growths are legibly preserved. ‘The number of the woody layers 
indicates the number of the generations which have perished, i. €-, 
ment of a vigorous season, an indistinct one of a bad season, 4 
sickly one (which is often found among healthy ones) indicates 
the unhealthiness of the foliage of that particular year. The 
son of vegetation. 
The relations indicated above compel us to recognise a SUC 
cession of generations in trees, shrubs, and perennial herbs ; and 
* Beitr, p-152, where the following view of the arboraceous stem, as 4 common 
ground —— many individuals is developed ; but this whole view, after all, needs 
to be corrected by a precise limitation of its meaning by what follows it. 
