Physiological Points 17 
conditions. To this very important relation which exists 
between root and crown development we shall refer again 
further on. 
Instead of leaves, the youngest parts, 7.e., the tips of the 
roots, are beset with fine hairs; delicate structures which 
serve the purpose of taking up water. The root-hairs live 
only a very short time, hardly through the season, being 
ever replaced by new hairs near the tip, which constantly 
pushes into new soil. The tips of the roots, therefore, are 
the most important part of this organ for the life functions 
of the tree. 
Physiological Points. We may now take a brief glimpse 
into the household affairs of the tree, — the manner in which 
it lives. 
The essential fact which must be realized is, that the 
leaves and buds at one end, and the tips and youngest parts 
of the roots at the other end, with the cambium layer con- 
necting the two, are the living tissues, and hence the main 
factors in the household. The tips and youngest ends of 
the roots or rootlets, densely beset with little hairs, are the 
mechanism which takes up the water and minerals from 
the soil. These are conducted through the roots by way 
of the cambium and the younger wood and bark to the 
leaves. The leaves in turn take up carbonic acid from the 
air, decompose it in their green parts (chlorophyll) under 
the influence of light, and combine it with the minerals and 
water into food materials which can be used in building up 
the body of the tree. This process is called assimilation. 
The food materials, manufactured in the leaves, wander 
through the veins and stalks of the leaves into the cambium 
and the youngest wood and bark of the stem and root, 
where they are used in new growth during the season, making 
the annual ring, or else are stored (especially in the pith rays) 
