AMERICAN 
JOURNAL OF BOTANY 
Vol, V March, 191 8 No. 3 
A DEMONSTRATION OF PHOTOSYNTHESIS 
W. J. V. OSTERHOUT 
The difficulties in the way of a satisfactory demonstration of 
photosynthesis in land plants are too well known to require comment. 
They are greatest when quantitative results are desired. It is, of 
course, precisely these which are most important. 
It is taken for granted that the reader is familiar with methods 
now in use.^ The chief requisites appear to be (i) a method of remov- 
ing at intervals satisfactory samples of the gases by which the leaf is 
surrounded (to accomplish this it is necessary to stir and mix the gases 
before taking the sample). (2) A method of gas analysis, simple and 
sufficiently accurate. (3) It is desirable to avoid the use of mercury, 
since the leaf is easily injured by mercury vapoV. 
The simple apparatus here described seems to meet these require- 
ments and is easily* constructed and kept in order. Its special ad- 
vantage is that it permits the mixing of gases and the withdrawal of 
samples at will. In this way the progress of photosynthesis can be 
followed and the dynamics of the reaction investigated. It is also 
possible, when studying photosynthesis, to determine respiration 
without removing the leaf from the apparatus or changing the gases 
which surround it. 
The apparatus consists of a wide-mouthed bottle (figure i) or 
jar (the larger the better, up to a capacity of one gallon) with a stopper 
perforated by three or more short glass tubes (R). Each of these 
is connected (by rubber tubing) to a short glass tube (5) directly 
above it. This is in turn connected (by rubber tubing) to a tube 
about two feet long, (A), which is held in a vertical position by an 
arm (T) of a ring-stand. This tube should be of at least 9 mm. 
^ Cf. Ganong, W. F. Plant Physiology, 107 ff. 1908. 
[The Journal for February (5: 55-104) was issued March 9, 1918.] 
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