1910. | On Vegetable Assemilation and Respiration. All 
by proving that there have been no facts brought in support of the con- 
ception of optima in connection with assimilation which are not more 
harmoniously interpreted on the theory of the interaction of limiting factors. 
Section V.— CONCLUSIONS. 
1. The experiments on assimilation in water-plants dealt with in this paper 
are carried out by a new method which takes account of the alteration of 
the gases in solution as well as of the gases liberated as bubbles. 
2. The aim of this study is to demonstrate the nature of the relation 
between assimilation and the chief environmental factors; (1) COs-supply, 
(2) light-intensity, and (3) temperature. The relation is such that the magni- 
tude of this function in every combination of these factors is determined by one 
or other of them acting as a limating factor. 
3. The identification of the particular limiting factor in any definite case 
is carried out by applying experimentally the following general principle. 
When the magnitude of a function rs limited by one of a set of possible factors, 
ancrease of that factor, and of that one alone, will be found to bring about an 
ancrease of the magnitude of the function. 
4, Two long series of experiments with Elodea and with Fontinalis have 
been carried out in which the light and temperature remained constant 
while the COse-supply varied through a wide range (from 0°0025 to 
0:0540 grm. COz per 100 c.c. of water). | 
In both series the same phenomena is observed ; at first the assimilation 
increases steadily in proportion to the increase of the COQ2-supply and then 
abruptly this increase comes to a stop, at a value of about 0°023 grm. CQ: 
assimilated per hour. This is shown to be the limit set by the particular 
intensity of light adopted and, without more light, no further increase of 
COz2 will bring the assimilation above this level. 
5. The form of curve obtained is a typical “compound hmiting factor 
curve”; there is no sign of an optimum or of ultra-optimal depression of 
assimilation even when water one-third saturated with COs is employed. 
The first phase only of this curve exhibits the significant primary relation 
between CO2-supply and assimilation, and it is clear that here the magnitude 
of assimilation varies in direct proportion to the CO:-supply. 
6. Incidentally it comes out that the Bryophyte, Fontinalis, is consistently 
less efficient in the intake of CO. than the submerged Phanerogam, Elodea. 
This is possibly correlated with the absence of any “internal atmosphere ” 
in the former. 
7. From the data obtained in this research there is constructed a diagram, 
