Influence of Certain Carbohydrates on Green Plants 57 



trations of maltose had to be discarded, in the one case because of 

 contamination and in the other case because only one plant developed. 

 The results are given in table 24. 



It is interesting to note that here again there is a marked effect on 

 growth with increase in concentration, and furthermore that a concen- 

 tration of maltose as low as 0.4 per cent is capable of influencing the 

 yield of dry matter. It should be borne in mind, also, that the plants 

 are in the seedling stage, when there has been available for them a con- 

 siderable reserve supply from the cotyledons. 



As was noted in many of the cultures, the addition of sugar gave rise 

 to a production of color in the stalk. The check cultures, lacking sugar, 

 produced plants with green stems, these being entirely devoid of the 

 characteristic purplish pigment except at the base. The sugar-fed plants, 

 on the other hand, were distinguished by the production of high color, 

 and there was a gradation in intensity of color according to the con- 

 centration of the sugar. 



ABSORPTION OF SUGAR FROM DILUTE SOLUTIONS 



In the preceding experiments the lowest concentration employed was 

 0.1 per cent. As has already been stated, this is a relatively high con- 

 centration and one that is undoubtedly never attained in the soil solution. 

 If the organic material in the soil is directly available to the higher plants, 

 the substances must be absorbed from extremely dilute solutions, for the 

 organic content of the soil solution is very small. But, while the con- 

 centration of the organic matter in the soil solution is extremely low, 

 yet there must be a constant supply of soluble organic matter available 

 to support the bacterial and the fungous flora. 



The ability of the higher plants to absorb solutes from weak solutions 

 has been amply proved for the nutrient and the non-nutrient salts as well 

 as for dyes. All the nutrient salts are present in extremely dilute con- 

 centration in the soil solution. The mere fact that the amount of organic 

 matter dissolved in the soil solution is extremely small is not a barrier 

 to the utilization by the plant of the dissolved organic substances. The 

 ability of vetch to remove glucose from a weak solution was tested by 

 means of the following experiment : . 



Ten culture vessels were prepared, each containing 50 cubic centimeters 

 of 0.0005 gram molecular glucose. Four of these were kept as checks. 



