Carbon Assimilation. 
'59 
In order to examine the intake of carbon dioxide by submerged 
water plants, a stream of water containing carbon dioxide dissolved 
in it was passed over the leaf. By estimations of the carbon dioxide 
that bad passed over the leaf in a definite period the rate of intake 
of the gas could be measured. The procedure employed with land 
plants was somewhat modified. A description of the method is 
given in the eighth paper in Blackman’s series of researches 
(Blackman and Smith, 1911 a). 
With small-leaved plants such as Fontinalis and Elodea, sprigs 
of the plant were used instead of single leaves as in experiments 
with Cherry Laurel or Helianthus. In most of the experiments 
medium temperatures and medium illumination were employed. 
The value taken for the carbon dioxide supply is the mean value of 
the carbon dioxide concentrations of the liquid before and after 
passage through the chamber. The ‘ real ’ assimilation was 
calculated as in the experiments with land plants already described. 
The results obtained with both Fontinalis and Elodea are 
shown in the accompanying curves (Fig. 13). In the weaker 
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Carbon dioxide supply in grams of C0 2 per 100 c.c. water. 
Fig. 13. Curves illustrating the influence of the magnitude of carbon 
dioxide supply on assimilation. E, Elodea ; F, Fontinalis (after Blackman and 
Smith). 
solutions of carbon dioxide, the assimilation increases directly 
with increase of carbon dioxide supply. Neither light nor temper¬ 
ature are limiting. In each case, however, a point is reached where 
increase in carbon dioxide supply is no longer accompanied by a 
corresponding increase in assimilation. The latter remains constant 
however much the carbon dioxide supply is increased. Here, 
either temperature or illumination is limiting the rate of assimilation. 
