re of cambium tissue gives us a clearer conception of
its extreme delicacy. It is one of the most sensitive and delicate
substances in all nature. Exposure to the air will kill it and
completely destroy its functions in a few seconds. It is easily crushed
by slight pressure and quickly killed by exposure to drying, frost,
moisture and sunlight. Nature shows her extreme care of it for in making
bark she has formed for the delicate cambium a perfect protective
covering. Like the cambium the bark is composed of cells, as in fact are
all animal and vegetable structures. But the cells of the bark have
thick walls of a tough, corky substance, and each cell contains air
instead of protoplasm. The corkiness of the bark makes it an impervious,
waterproof covering that does not allow the cambium to be dried out or
to be washed by external moisture. The air in the bark cells being in a
still condition is a non-conductor of heat, and layer of bark
overlapping layer, the cambium is completely covered with a dead-air
blanket. This keeps it from being frozen in winter and from being
overheated in summer, just as a dead-air space in the walls of a
building protects from extremes of heat and cold. From this it is plain
that nature takes great pains to cover and protect the delicate cambium
from all external influences. This stands in striking contrast to the
careless manner in which many propagators and planters handle the
delicate parts of trees. It also explains why some budders get such a
small percentage of living buds and some planters so few living trees.

Cambium is the building material of plants and without it growth is
impossible. It covers every portion of the tree from the topmost
terminal bud to the deepest root tip like a living blanket. During the
growing season the cambium cells divide lengthwise forming new cells.
These divide again and grow, and new cells are formed, until by fall a
complete mantle of bark covers the outer surface of the cambium, while
within it has built up a solid layer of the woody structure of the tree.
A few rows of cambium cells are left in an embryonic condition to carry
on growth the following year. The cambium is thus the only tissue of the
tree that retains from year to year the power of active growth. The
layers of wood and bark, after performing their functions for a few
seasons, gradually die and are overlapped by new layers, but the
cambium remains living throughout the entire life of the