5i 
protected from evaporation in stem and flower that we may find 
plants still standing upright in the ground, flowering and ripening 
their seed, although the root and lower part of the stem with 
the leaves on it are dead and brittle. Others, of the portulaca 
family, are so retentive of life that they may be used for room 
decoration without water for weeks or months, while under 
heavy pressure within sheets of drying paper they continue their 
growth for long periods. 
As the leaf is the respiratory organ of the plant, besides being 
concerned in transpiration, its formation and intimate structure 
are important objects of study. The leaves are in direct con- 
tinuity with the roots through the medium of the vascular fibres, 
which pass from the roots through stem and branches, and from 
these through the stalk of the leaf, breaking up on entering its 
blade into an expanded network visible to the naked eye, so that 
every minute portion of its area is supplied with water. The 
surface of the leaf is studded over with minute pores, which allow 
the water to escape into the air as vapor, and at the same time 
let in the air for respiratory purposes. The small cavities to 
which the pores or stomata give access are lined with delicate 
living cells which are the active agents in the function of re- 
spiration or breathing. The carbonic acid gas entering with the 
air becomes dissolved in the water that has ascended from the 
roots, and is thus presented to the active living cells which 
decompose it into the oxygen which escapes into the atmosphere, 
and the carbon which is appropriated for the formation of the 
woody tissue of the plant. The breathing pores or stomata ar so 
affected by the state of the atmosphere that when it is very dry 
the two cells guarding them so alter their form and position as to 
close the opening, while with a moist atmosphere and a full 
current of sap flowing they become more turgid and bulge out* 
wards so as to form an opening that allows communication with 
the air again. It can be well understood that in a dry climate 
a large distilling apparatus of the kind indicated would not 
generally be suitable ; for lack of moisture it could not be kept 
in action. The extensive scale on which broad-leaved trees in a 
moist atmosphere transfer water raised from the ground to the 
air has to be reduced, so that the quantity exhaled shall be 
proportioned to the amount present in the soil. Accordingly 
the broad leaves, with innumerable breathing pores, must have 
their surface diminished in extent, and the cellular tissue and 
stomata reduced in proportion. In conformity with this require- 
ment we find that in a very large number of our local plants the 
foliage is of a very stiff, spiny, and harsh character, the soft 
cellular tissues being reduced to a minimum, the leaves being 
narrow, with prominent ribs, and ending in sharp points. 
As we have a copious rainfall in the winter months, a luxuriant 
growth of some broad -leaved plants is encouraged, but the 
