CHEMICAL CONSTITUTION OF FRUITS. 847 
same year in which they are developed afterwards perish, from 
the exhaustion of nutrient matter thus occasioned ; and that 
such is the reason is proved by the fact, that we can make 
annuals biennial, or even perennial, by plucking off the flower- 
buds as they are successively developed. Some plants which 
only flower once require many years to accumulate sufficient 
nourishment to support the processes of reproduction. Such are 
the American Aloe (Agave americana) and the Talipot Palm 
(Corypha umbraculifera), both of which live many years before 
flowering, after which they die. A bad fruit year is also 
generally succeeded by a good one, and vice versd, because in 
the former case an additional supply of nutrient matter is 
stored up for the fruiting season, and in the latter there is 
a diminishel amount. Again, if a branch of an unproductive 
tree have a ring of bark removed so as to prevent the down- 
ward flow of the elaborated sap, its accumulation above will 
cause the plant to bear much fruit. Pruning depends for its 
success upon similar principles. In order to obtain good fruit 
it is also necessary not to allow too many fruits to come to per- 
fection on the same plant. Other matters connected with this 
exhaustion by fruiting have been already alluded to, in speaking 
of Annual, Biennial, and Perennial Roots, at page 133. 
The changes produced upon the atmosphere in the ripening 
of the fruit, depend upon the nature of the pericarp. Thus, 
when the pericarp preserves its green state, as also always when 
first formed, it has an action similar to that of the leaves ; but 
when of other colours than green, and more especially when 
succulent, it evolves carbon dioxide at all times, instead of 
oxygen. 
Chemical Constitution of Fruits.—The chemical constitution 
of fruits varies accoidinyz to their nature and age. When the 
pericarp is of a dry na‘ure, it commonly assumes a whitish or 
brownish colour, and its cells become thickened with hardened 
matters, and their cellulose walls converted into lignin. Under 
such circumstances, no further changes take place in its chemical 
constitution, and its vital activity ceases. But when the peri- 
carp becomes succulent whilst ripening, it assumes various 
tints ; transpiration goes on from its outer cells, the contents of 
which thus become dense, and absorb the watery matters from 
those within them ; these in like manner react upon the contents 
of those within them, and so there is a constant passage of fluid 
matters from the surrounding parts by osmotic action into the 
pericarp ; in this way, therefore, it continues to enlarge, until it 
has arrived at maturity, when transpiration nearly ceases from 
the deposition of waxy matter in or upon the epidermal cells, 
and the stalk by which it is attached to the plant becomes dried 
up. When first formed such pericarps have a like composition 
with leaves, and but little or no taste. After a time they ac- 
quire an acid flavour from the formation of vegetable acids, and 
