1916] CURRENT LITERATURE 421 
factor into the BaEyER hypothesis, to which altogether too much attention 
has been paid by chemists and physiologists. 
The reviewer feels that the results of the chemist Wrisritrer, who, to 
paraphrase a statement of JOHANNSEN’s, carries on his physiological studies 
not as chemistry, but with chemistry, deserve the notice of all physiologists 
and chemists, and are full of promise of a new attack upon the most funda- 
mental material problem of mankind, namely, the increase of the food supply 
of the world.—G. K. K. Linx. 
The bubble method in photosynthesis.—KnieP’ has made a critical study 
of the value of the bubble method for comparing the rate of photosynthesis 
in water plants under various conditions. From his work it is evident that the 
method must be applied with great caution. Part I deals with the percentage 
of oxygen in eliminated gas bubbles. This percentage rises as the rate of bub- 
bling increases, but not in direct proportion. If one were to find the total 
oxygen production due to photosynthesis, he would need to determine (1) 
the volume of the eliminated gas with its percentage of oxygen, and (2) the 
amount of oxygen that diffused into the bathing water. For the analysis of 
eliminated gas Kniep used Krogh’s apparatus, by which the percentage of 
oxygen and carbon dioxide can be determined in very small samples of 4-6 mm.3 
The amount of oxygen diffusing into the bathing water was determined before 
and after a period of photosynthesis by WINKLER’s titration method. The 
percentage of oxygen in the eliminated gas varied from 22.8 per cent in slow 
Photosynthesis to 45 per cent in rapid photosynthesis. 
e whole matter is complex. The oxygen production in photosynthesis 
not only increases the volume of gas in the intercellular spaces and leads to 
elimination of gas from the cut surface of the stem, but it increases the oxygen 
percentage in these spaces and thereby steepens or sets up diffusion gradients 
(falling gradient of oxygen from intercellular spaces to bathing water and of 
nitrogen in the opposite direction). -Carbon dioxide diffusion gradients due 
to its consumption must be considered also. Hence the amount of gas given 
off as bubbles and its richness in oxygen and other gases is the resultant of all 
these processes acting together, a given set of conditions giving one equilibrium 
and a change in conditions gradually leading to another set of conditions. 
Part II presents the influence of water movement upon the bubble outgo. 
With 1 per cent KHCO, in distilled water as the bathing medium, water move- 
ment temporarily stops the bubble outgo. With tap water (supersaturated) 
the outgo of bubbles increases and continues in darkness even in dead plants. 
This behavior is all explained on the basis of the éffect of the water movement 
upon the gas gradients. On the basis of these results KNnreP pointed out the 
3 KnIEp, s, Uber den Gasaustausch der Wasserpflanzen. Ein Beitriige zur 
Kutik der Srmcateomton Jahrb. Wiss. Bot. 56:460-509. 1915. PFEFFER’S 
Festschrift. 
