PLANT NUTRITION. 35 
chlorophyll. Lastly, there is the class of true parasites, 
such as the broom-rapes (Orobanche) and dodders (Cus- 
cuta), which affix themselves to living plants, and being 
. themselves destitute of chlorophyll, are unable to live, 
except at the expense of the plants upon which they 
grow. 
Transpiration of Water.—There is a large absorption 
of water, as has been said, by means of the root, and in 
some cases, at any rate, there is an absorption of the 
same fluid or vapor by means of the leaves. On the other 
hand, there is a loss of water or watery vapor from the 
surface, which is sometimes so profuse as to cause the 
plant to wither and flag. We have only to place some 
leaves in a cool tumbler, and expose them to the light, 
to see the condensed water on the sides of-the glass. 
The quantity of watery vapor emitted in sunlight by the 
green surfaces of plants is enormous, and it has been 
shown experimentally that it is the chlorophyll which is 
largely concerned in this outflow, for where that sub- 
stance is deficient and wanting, transpiration of fluid is 
proportionately reduced or stopped. But while bright 
light, such as that furnished by the red and yellow ray 
of the solar spectrum, is most efficacious in stimulating 
the decomposition of carbonic acid, it is the blue ray 
which specially favors transpiration of the fluid. <A high 
degree of temperature, as might be expected, favors 
transpiration, as does also a dry state of the atmosphere. 
The condition of the plant, its age, and other circum- 
stances are also important agents in regulating the 
amount of transpiration. 
Some idea of the amount of water given off may be 
gleaned from some experiments made by Sir John Lawes, 
and recorded in the ‘‘Journal” of the Horticultural 
Society for 1850, thus—During one hundred and seventy- 
two days, March 19 to” September 7, the total weight of 
