152 Mr. E. H. Acton. The Assimilation of Carbon 



tions on shoots {vide groups A and C in detailed account) where 

 Meyer has obtained positive results. 



I am indebted to Professor S. H. Vines for the suggestion to 

 experiment with an "extiact of natural humus " (see No. 12, p. 172). 



Methods and Apparatus Employed. 



The experiments with each of the substances employed are classified 

 as follows : — 



A. Experiments with cut branches. 



B. Experiments with solutions supplied to the Toots of plants 

 placed in a culture liquid, or in a few cases in sand moistened with 

 the same. 



C. Experiments where the solutions were applied externally by 

 placing on the upper surfaces of leaves. 



All the investigations were made as far as possible with plants, 

 shoots, leaves, &c, in a healthy condition, and results are not stated 

 in any cases where there was reason to believe that the plants, &c, 

 had been injured by preliminary manipulations or exceptionally un- 

 favourable conditions during the progress of the trials. 



As is generally the case in experiments with culture solutions, algse, 

 fungi, &c, often developed in the solutions, although the cylinders 

 were surrounded with black paper and the liquids had been pre- 

 viously boiled ; where this occurred to any considerable extent the 

 cultures were repeated with fresh plants. In a few cases the roots 

 of the plants were placed in damp sand and the sand moistened 

 with the substances in use. The sand had been strongly heated in a 

 muffle just before using. The words " sand culture," placed against 

 some of the results in the detailed account, signify that this method 

 had been used instead of the ordinary water culture. 



To deprive the leaves and tissues of starcn at the beginning of the 

 experiments, two methods were resorted to : — 



(1.) Placing in the dark until portions of the leaves were shown 

 by testing to be completely free from starch. 



(2.) Placing under a bell-jar with substances which entirely remove 

 all C0 2 from the air until the same result was obtained. Of these 

 methods the latter was fonnd to be the more convenient and used in 

 nearly all cases. In the case of seedling plants the cotyledons must 

 obviously be removed before placing under the bell-jar ; but this 

 operation need not cause any injury to the plant if carefully per- 

 formed and the young plant has formed sufficient ordinary foliage 

 leaves to be independent of the cotyledons. The apparatus used was 

 as described on p. 154, and is represented in section by diagram ~No. 1 

 on the opposite page. 



In this apparatus the branches, shoots, &c, freshly cut off under 



