January 14, 1898.] 



SGIENGE. 



45 



tion aud is conducted directly to the leaf 

 by means of the circulation of the plant 

 itself. This water, the mineral and nitrog- 

 enous matters which it contains in solu- 

 tion, and the carbon dioxid which enters 

 from the air, are the raw materials which 

 by plant metabolism are changed into the 

 tissues of the living vegetable. 



The source of energy, by means of which 

 this wonderful chemical synthesis is pro- 

 duced, is the heat and light coming from 

 the sun. Green is of the opinion that for- 

 maldehyd is one of the first products of the 

 condensation of the carbon dioxid, but as 

 formaldehyd is essentially a poison and a 

 preservative it is not probable that its ex- 

 istence is more than momentary. It may 

 be that formaldehyd is one of the transi- 

 tory products of vegetable metabolism, but 

 it cannot be regarded as being produced in 

 any considerable quantities or existing for 

 any length of time. 



The final and possibly the direct product 

 of the condensation is some form of sugar. 

 The production of these reserve stores of 

 food, viz., carbohydrates, proteids and fats 

 in quantities largely in excess of those 

 necessary for the growth of the plant itself 

 are fully discussed, and the very latest 

 views concerning the methods of storage and 

 subsequent use of these materials clearly 

 pointed out. 



Investigations of marked interest have 

 lately been conducted on the properties and 

 functions of humus. Hilgard has shown 

 that the nitrogen content of humus found 

 in the soil of the California Agricultural 

 Experiment Station is as much as 18 per 

 cent, in the virgin state. The content of 

 nitrogen in the humus by after years' culture 

 was reduced from 18 to 3 per cent. In the 

 meanwhile, however, the total percentage 

 of humus in the soil had slightly in- 

 creased. 



The obvious conclusion to be drawn from 

 these researches is that the fertility of a 



soil, in respect of its humus, does not de" 

 pend so much on the actual percentage of 

 humus itself as upon the nitrogen content 

 therein. When a plant, therefore, gives 

 evidence of nitrogen hunger it is not always 

 due to a deficiency of humus, but probably 

 rather to the diminution of the nitrogen 

 content of the humus. 



A more striking example came to Hil- 

 gard's attention in a soil from Hawaii, 

 which, after three years of cultivation, gave 

 evidence of marked deficiency in the ni- 

 trogen ration of the plant. The virgin soil 

 showed a content of 10 per cent, of humus, 

 which is far above the average of even fer- 

 tile soils. On analysis, however, it was 

 found that the nitrogen content of the 

 humus had been reduced to 1.7 per cent. 

 It is concluded from the observations of the 

 deportment of crops on soils of this kind 

 that wherever the nitrogen in the humus 

 of the soil falls below 2.5 per cent, of the 

 total weight of the humus the crop will 

 show evidences of nitrogen hunger. 



Snyder has shown that in sterilized sand 

 oats will not grow when fed with humus in 

 which no nitrifying ferments are present. 

 If, however, the nitrifying ferments be ad- 

 ded in the form of leachings from an arable 

 soil the oats will grow and develop in the 

 usual manner. 



Snyder has also shown, as a result of his 

 investigations, that humus acts not only in 

 supplying the elements of fertility, but also 

 in combining with mineral matters, espe- 

 cially potash, producing in the soil potas- 

 sium humates and rendering the potash 

 thus more easily assimilable. In other 

 words, the humus acts in a favorable man- 

 ner by converting the inert plant food of 

 the soil into a form in which it can be ab- 

 sorbed. The experiments in sterilized pots 

 show that the humates of potassium, magne- 

 sium and iron and the double humates of 

 phosphorus and sulfur can be utilized di- 

 rectly as plant food, provided nitrifying 



