66 OUR WOODLAND TREES. 
branches, of the leaves, of the flower, and of the 
fruit or seed. 
Beginning with the root, we have seen that its 
incipient form consists of an elongation of the 
radicle of the embryo. Development takes place 
by continued elongation and branching, the 
branches being at first very thin and minute. 
As we know that a certain density of the soil 
is essential to healthy plant life, we arrive at the 
conclusion that the conditions most favourable 
to root growth are those in which the embryo 
plant is surrounded by particles of earth having 
just sufficient porousness to admit a certain 
amount of air, and to permit the percolation of 
water. The root fibres, or filaments, which are 
at first the most delicate of threads, are pushed 
out by the power of growth from the root-stock 
or radicle of the plantlet, and insinuate them- 
selves into the tiniest of the surrounding earthy 
interstices. Receiving nourishment from the 
damp soil through the medium of the root hairs— 
long, hollow cells, which absorb moisture by 
capillary attraction—they rapidly become en- 
