389 
Hxperimental Researches on Vegetable Assimilation and Respira- 
toon. IX.—On Assimelation in Submerged Water-Plants, 
and its Relation to the Concentration of Carbon Dioamde and 
other Factors. 
By F. Frost BiackmaN, D.Sc., F.R.S., Fellow of St. John’s College, 
Cambridge, and Reader in Botany in the University; and A. M. Smiru, 
M.A., formerly Senior Demonstrator in Botany in the University of 
Cambridge. 
(Received December 19, 1910,—Read February 9, 1911.) 
CONTENTS. 
PAGE 
HeraUGHO CC ENO Mies me yee te sie eek ete onaicio siren tosis cea aisiue'sadinsem ee ace ceunennee 389 
Section I.—Relation of Assimilation and CO,-Supply................000e 390 
- ie Sulb nonmalpASsimlatiOM “scceass.cccscecensesecaasaveversee ste 395 
i Ti —Interaction of Mimiting Factors .c....0<...<scsacesveveotenese 396 
5 IV.—Critical Analysis of Results of Previous Workers......... 403 
is WiC OM CIUSIONS | Seances ters cee caacaaeveceesas coda caicne seine’ voce eigeaues A411 
INTRODUCTION. 
The fourth paper of this series* contained an account of quantitative 
investigations on the magnitude of assimilation in the leaves of land-plants 
under different conditions of illumination and temperature. 
The general conclusion reached was that the actual magnitude of 
assimilation in a leaf at any moment is determined by one or other of the 
main controlling conditions, light, temperature, or COs-supply, acting as a 
limiting factor.t 
_ Since then it has been thought desirable to attempt a quantitative study 
of the assimilation in submerged water-plants on similar lines, and in 
particular to study the relation of assimilation to CO2-supply, a subject which 
had been left on one side in the work on land-plants. 
A preliminary difficulty was the absence of any satisfactory method of 
measuring, through a wide range of conditions, the assimilation of plants 
submerged in water. This difficulty has been removed by a new procedure 
which we have described in the previous paper of this series.| We may now 
proceed to consider some of the results obtained in this way. 
The first section will deal with the factor of CO2-supply, and the succeeding 
* Blackman and Matthaei, ‘ Roy. Soc. Proc.,’ B, 1905, vol. 76, p. 402. 
+ Blackman, ‘Optima and Limiting Factors,” ‘ Annals of Botany,’ 1905, vol. 19, p. 281. 
{ Blackman and Smith, “ Assim. and Resp., VIII,” ‘Roy. Soc. Proc.,’ B, 1911, p. 374. 
