74 OUR WOODLAND TREES. 
the substance which makes up their soli¢ bulk. 
Carbonic acid gas—a combination of carbon and 
oxygen, largely contributed by respiration from 
animal lungs—is diffused throughout the atmos- 
phere. Leaves, through their breathing pores, 
inspire this gas, appropriate for purposes of 
development and growth the carbon of the com- 
pound, and return the life-giving oxygen to the 
air, to add to the healthfulness of their sur- 
roundings. The glorious sunshine, which adds 
its golden hue to foliage, contributes its action 
—action mysterious though beautiful—to stimu- 
late the process; so that there is co-operation 
in this marvellous work of usefulness between 
two of the most beautiful of the forces of 
Nature. 
At a certain stage of growth—varying in dif- 
ferent species of Trees and in different indi- 
viduals of the same species—commences the 
production of the flower and the formation of 
the seed which is to follow the foretelling bloom. 
The blossoming of a Tree is not, as in go many 
other plants, the precursor of decline and decay ; 
nor is this period of its life the sign of perfection; 
