Experimental researches on vegetable assimilation and respira­tion. VI.—Some experiments on assimilation in the open air

Abstract

In investigating assimilation under natural conditions, gasometric methods, which involve enclosing leaves, are unsuitable. The only method which is free from this objection is the half-leaf dry-weight method introduced by Sachs. Unfortunately, owing to the overlooking of certain grave errors to which this method is liable, most of the earlier work is of uncertain value. Having, however, made a full investigation into the sources and magnitude of these errors, an account of which was published in an earlier paper, I have been able, after introducing appropriate modifications, to use the method with precision, and to obtain results whose degree of approximation to the truth can be justly gauged. The vexed question of the highest rate of assimilation possible to detached leaves of Helianthus annuus in the open air first claimed attention. Measurements of the gain of dry weight by these leaves on bright sunny days (described in Section II) have clearly proved that Sachs’ original value was not excessive, and suggest some of the conditions which must be fulfilled if such assimilation is to be possible.