66 
tinued by the chemical action which leads the gas produced to find its 
way out of the call in the direction in which that particular gas finds a 
way opened for it by exosmosis. As these actions proceed, the cell 
becom2s changed in its character. The cell either doubles itself, or is 
developed into some other form of tissue, or it becomes filled with 
formed material or dead tissue which may be the special product of 
the plant. There is multiplication of bioplasm first, as shown by 
deduplication of cell life, and subsequently formed material is laid 
down in readiness for the nourishment of the bioplasm which is 
about to become dormant. Bioplasm requires light, warmth, and 
moisture to bring out its vitality, and if one or all of these be absent 
or deficient in amount a new birth does not arise—a cyclosis is not 
setup. This, however, is not the circulation of sap as ordinarily 
understood ; but it is the way in which plant life commences and is 
renewed every spring. If light, warmth, moisture, and air are 
fortheoming, the two iatter supply material which is combined with . 
the pabulum already in the seed; growth is promoted, and circula- 
tion arises. Trees might be considered as hybernating in the 
winter, circulation being reduced to a minimum ; but a living tree 
is warmer than a dead tree, as might be seen trom the snow melting 
sooner on it than on the latter. Not only a circulation but a 
respiration goes on all the year ronnd, and minute quantities of 
carbonic acid are yiven out by a tree from all parts of its structure. 
Directly leaves are produced they begin their proper functions, 
which are to act as exhaling organs, giving out watery vapour to 
the air, and with it the oxygen that has been set free by the act of 
growth. ‘This exhalation of moisture necessitates the abstraction of 
liquid from below. ‘The cellular and libro vascular tissue of the 
tree itself parts with liquid; a current is established from below 
upwards in each cell, and an endosmosis arises. A powerful vis a 
fronte is set in motion lke that of a pump at millions of 
points on the tree, which becomes an irresistible force in raising 
fluids from below upwards. This action rapidly extends downwards 
from the buds and leaves to the roots of the tree. It is not, 
however, by a vis a fronte alone that the circulation is carried on, - 
There is a vis a tergo as well which acts as powerfully. The earth 
receives and retains its warmth more persistently than do the 
buds. Heat is not lost so rapldly as it in the buds themselves. A 
new vitality arises in the roots as well as in the branches, com- 
mencing earlier than that which begins in the buds. New life 
develops at the extremity of each fibre below the ground. Each 
extreme cell contains dormant protoplasm as well as the buds, and 
with returning sprihg there is new growth. ‘Trees cast off minute 
hair-like processes from on the fibrille of the roots every 
autumn. As soon as the function of the leaf ceases, the rapid 
absorption of aqueous matter is no longer required; and one of the 
great advantages which attend upon the equinoctial gales and the 
ta nt ee 
