W. J. V. OSTERHOUT AND A. R. C. HAAS 6 



diffusion from the air. The amount of COo at the immediate disposal 

 of the plant therefore depends largely on the amount of carbonates 

 and bicarbonates present. 



The usefulness of carbonates and bicarbonates in this connection 

 is greatly increased by the fact that the plants are able to split them 

 so as to extract from them much more CO2 than can be removed by 

 bubbling a stream of hydrogen through the solution. 



In order to measure the degree of alkalinity produced by Ulva, a 

 piece of the frond was placed in a tube of Pyrex glass^ (about 12 mm. 

 in diameter and about 5 cm. long) in such a manner that it completely 

 covered the inside of the tube for the greater portion of its length. 

 Fronds were chosen which were sufficiently stiff, so that their own elas- 

 ticity caused them to remain pressed against the inner surface of the 

 glass tube even when liquid was poured in and out or shaken back and 

 forth in the tube. 



The glass tube was sealed off at one end, while at the other it was 

 furnished with a short piece of rubber tubing covered with paraffin.^ 

 The covering of paraffin was continuous and care was taken to renew 

 it frequently. 



After placing the frond in the tube, the latter was filled with sea 

 water containing indicator'' and the rubber tube was clamped shut. 

 In some cases a small bubble of air was left in the tube to act as a 

 stirrer; in other cases the tube was completely filled with sea water 

 and the stirring was effected by a small piece of paraffin or by a glass 

 bead covered with paraffin. 



In order to determine the degree of alkalinity produced by photo- 

 synthesis two methods were used. In the first, the indicator was 

 added to the sea water containing Ulva after a definite exposure to 



^ This glass was chosen because it does not give off measurable quantities of 

 alkali during the period of the experiment. 



^ It is necessary to use paraffin which will not give off measurable quantities 

 of acid during the time of the experiment. For this purpose paraffin of a high 

 melting point is usually advantageous. Rubber should be used which gives off 

 the minimum amount of acid ; the rubber used in these experiments was repeatedly 

 boiled before using. 



^ Ten drops of saturated alcoholic phenolphthalein was added to 1 Hter of 

 sea water. This makes the concentration of alcohol 0.0067 m and that of phenol- 

 phthalein 0.0001 M. 



