434 
Baker . — Quantitative Experiments on 
proportion of carbon dioxide (about 80 per cent.) is evolved after the 
cotyledons have emerged. In the present investigation no constant gain 
in weight of the seeds has been detected, which could be attributed to 
absorption of oxygen ; this may be due to the comparatively prolonged 
experiments. Day, on the other hand, did not take into account the gain 
in dry weight due to the hydrolysis of his seeds, which has been found to 
be such an important factor in these experiments. 
Quantitative Experiments on the Formaldehyde Problem 
(see p. 426). 
Having found the relation between the loss in weight of the plants and 
the amount of carbon dioxide evolved by them in respiration under normal 
conditions, it was possible to proceed to investigate the question : Is form- 
aldehyde a step in respiration and converted by the plant into carbon 
dioxide, or is it merely a step in photosynthesis, requiring light energy for 
its further elaboration ? 
General Experimental Methods. 
The apparatus used is shown diagrammatically in Text-fig. 4 (p. 427). 
It consists fundamentally of the ordinary respiration apparatus, with 
arrangements for introducing small traces of formaldehyde into the air and 
for removing it again quantitatively. 
In these experiments two exactly similar cultures, with desiccators, &c., 
of the same dimensions, were grown simultaneously. In one culture the 
formaldehyde was introduced into the air before it passed over the cultures ; 
in the other ‘ check * experiment it was introduced immediately after the air 
had passed the calcium chloride tube. When the air had been quantitatively 
freed from formaldehyde and any other volatile substance used to condense 
this, the ‘ check ’ experiment should show exactly the same weight relations 
between the loss in weight of the plants and the carbon dioxide evolved 
during respiration as was found in the earlier respiration experiments. 
The general method of procedure was exactly the same as in these 
experiments (see p. 428 et seq.). 
A great many experiments were made before the quantitative absorption 
of formaldehyde could be satisfactorily accomplished. A short account of 
these may perhaps be given before proceeding to the final method used, as 
they not only indicate some of the difficulties involved, but also some of 
the capabilities and dangers of the gravimetric method of plant physiology. 
Experiments in which Chemical Absorbents for Formaldehyde were used. 
There are two general chemical methods for the estimation of form- 
aldehyde. One depends on its oxidation to formic acid. This is obviously 
