Bespiration and Cell Energy. 
407 
carbon-dioxide is not available in metabolism, and metabolism is continued 
without it, that is, without the formation of a carbohydrate and with the 
end product of carbon-dioxide. It is difficult to imagine that photo- 
synthesis is a separate and distinct process carried on by the protoplasm 
in addition to its ordinary metabolism. The exact function of the 
chlorophyll is not known, but it must be noted that chlorophyll and light 
are secondary factors in the metabolism. The prime factor is undoubtedly 
the living protoplasm whose own metabolism is included in that of the 
whole cell. 
The first aim of the green cells is to make food for themselves and 
then to form an excess for translocation to other parts of the plant where 
required. Some of the excess may be stored away in different organs for 
future use. The formation of an excess has become a necessity in all 
complex plants. In fact this must have been one of the first steps in the 
differentiation of plant tissues— cells set apart for different purposes must 
have food supplied to them. In plants like Spirogyra each cell makes its 
own carbohydrate with very little excess. It has been calculated that in 
a laurel leaf the amount of carbohydrate formed in any given time is about 
thirty times as great as that required in the nutrition of the leaf cells. 
Also in a sunflower it has been found that 25 grams of starch are pro- 
duced on a summer day on a square metre of leaf surface. A large 
amount of such carbohydrate is stored away in the seeds, &c., of the 
plants concerned for future use. 
It is generally held that respiration is a distinct process involving 
changes taking place in a cell on account of the introduction of oxygen 
and such phrases as " respiratory material," "respiratory changes," and 
"respiratory organs" are in common use. Now oxygen is required in 
the ordinary metabolism of the protoplasm, and respiration cannot be 
considered as being a process apart from metabolism. In this paper 
respiration will be held to be simply the interchange of gases ; that is, 
the introduction of oxygen to a cell and the removal of carbon-dioxide from 
it, the other processes being considered as connected with the nutrition 
and well-being of the cell. 
Continuous metabolism is a prime property of all living protoplasm. 
It is present to a slight extent in the cells of resting bulbs, tubers, &c., 
and it is doubtful if it is entirely absent from the living cells of dry seeds 
and desiccated plants. The peculiarity of metabolism lies in the fact that 
decompositions and combinations go on in living cells which would not go 
on at ordinary temperatures outside the cell. Oxygen, &c., only operates 
on the substances in the cell when conveyed to them by the living 
protoplasm. The chemical actions, therefore, which take place in a 
living cell may be termed animate as compared with those that take place 
in dead matter, and which may be termed inanimate. The protoplasm 
