552 



been acquired by the soil or the plants, the amount varyinj; in a general 

 way with the amount of the green vegetation above referred to. 



In the second series, from August to October, to prevent the growth 

 of the green organisms the soil was covered with a layer of calcined 

 quartz sand. Oats, peas, nuistard, cress, and spurry were grown, and, 

 as before, pots were left without plants. There was no growth of tlie 

 mosses and alga* and no appreciable aoiuisition of nitr(»g«'n, save in the 

 case of the peas, Avhich in this series, as in the tirst, acc^uired a large 

 amount of nitrogen. 



On the fixation of nitrogen by the soil, A. Gautier and R Drouin 

 {C(>mi)t. rend., 113 [J'^ni). pp. '■^;jo-<^l^'j). — In partial agreement with 

 the investigations of SchKising, and Laurent above described, the 

 authors quote from Coiiipie.s rrndus, lOG (1888), \t\^. 1174, 1233, and 1234, 

 reports of former experiments by themselves in which the importatit 

 functions performed by alga* in aiding the accjuisition of nitrogen by 

 the soil and growing plants are shown. They do not, however, believe 

 that the presence of alga- is essential to this process. AVith the aid of 

 illustrations drawn from their own investigations an<l those of Pasteur 

 and l>erthelot they attempt an ex]»lanation of ditlerent i)roeesses in the 

 fixation of nitiogen, which may be l>rietly summed up as follows: By 

 reason of the porosity of the soil, and the juesence in the soil of oxi- 

 dizable organic substances (humus) and of ai'-ntbic microbes which c(m- 

 tiiuiously cause oxidati(Ui, a snudl (juantity of combined nitrogen is 

 fixed in the soil from the surrounding atmosphere. The preparatory 

 absor])tion of this nitrogen by the microbes is without doubt one of tlio 

 conditi(»ns of its oxidation. These organisms afterward give it out to 

 the soil in the form of organic and amide nitrogen. The alga*, nitrous 

 and nitric ferments, etv., in their turn take part in the fixation of these 

 residues. P.ut they do not ajjjiear to be indispensable to the process, 

 as was indicated by the exp«'riments of the authors, especially those in 

 which neitlu'r alga' n<)r nitric ferments were present. In this way are 

 explained thejiart i)erformed by humus materials, tlie usefulness of the 

 ventilation and cultivation of the soil, the non assimilation of nitrogen 

 by soils sterilized by heat or antiseptics (as long since obscrvetlby Ber- 

 thelot), and the infiuence of algjc growing on the surface of the soil. 

 To establish the fact that the alga- directly fix free nitrogen it would 

 be necessary to cultivate them in inclosed nu'«lia incapable of tixing 

 combined nitrogen, and to show under these c<»nditions the direct accu- 

 nuilation of nitrogen in the substance of these organisms. The organic 

 material which exists in all arable soils is the indisi)ensable interme- 

 diary of the fixation cM' the IVce or ammoniacal nitrogen of the atmos- 

 jdiere. 



For further discussionsof s<Hneof the jxiints involved in these inves- 

 tigations, see Cotnptcs trntliis, 113 (1891), p. 1059, and 114 (1892), p. 19. 



