920 EXPERIMENT STATION RECORD. 



more common place. As soon as these tubers were fully matured the 

 roots and top of the original cuttings began to dry up. When cuttings 

 were used in which no joints or nodes were placed under the soil the 

 tubers developed from the axils of the leaf in every case. It was dem- 

 onstrated that the aerial tubers would germinate and produce tops, but 

 the resulting tubers were never larger than those planted. 



Similar experiments were conducted with Stachys florid ana, in which 

 tubers were developed in the axils of the leaf even before the cuttings 

 had made root, but they were never produceil above ground. 



Increase of the nitrogen of the soil by white mustard, S. von 

 Kowerski (Inaug. Diss., Halle, 1895; abs. in Jour. Chem. Soc. [London], 

 72 (1897), No. 421, II, p. 590). — A number of pot experiments were made 

 in which white mustard was grown in 2 lots of arable soil containing 

 0.1149 and 0.1261 per cent of nitrogen, respectively. There were also 2 

 pots in which peas and mustard were grown together. The pots were 

 sterilized, but no attempt was made to maintain their sterility, the 

 whole experiment being conducted out of doors. Each of the pots 

 received an equal quantity of sodium nitrate as well as mineral manure 

 and each showed a gain of nitrogen. The gain was from 2 to 7 times 

 greater in the unsterilized than in the sterile soil, and there was also a 

 greater gain of nitrogen under the influence of nitrogenous manure 

 than when the soil was uumanured. The author concludes that the 

 fixation of free nitrogen took place through the influence of the micro- 

 organisms present in the soil, the white mustard itself not being able 

 to assimilate elementary nitrogen. Peas grown in rich soil do not 

 assimilate free nitrogen even when their roots bear well developed 

 tubercles. 



The permeability of tree trunks to gases, H. Devaux (Compt. 

 Bend. Acad. Sci. Paris, 125(1897), No. 23, pp. 979-982).— By means of a 

 specially devised apparatus the author has been able to observe a very 

 considerable gaseous exchange between tree trunks and the air. 



He found that on the larger trunks lenticels are abundant and they 

 are frequently larger and more open than on the smaller branches. In 

 some trees such as Picea excelsa and Populus alba the lenticels are well- 

 developed yet they are almost completely closed for the most of the 

 time. 



The author states that the crustaceous lichens which often cover tree 

 trunks do not sensibly affect the gaseous exchange through the lenticels. 



Root tubercles in water cultures, H. A. Weber (Jour. Amer. 

 Chem. Soc, 20 (1898), No. 1, pp. 9-12, fig. 1).—A form of apparatus that 

 has proved very efficient in studying the development of root tubercles 

 is described and figured. Plants can be grown in any kind of culture 

 medium. The apparatus secures a constant level and thorough aera- 

 tion of the culture medium and peas have been readily grown to fruit- 

 ing in it. 



An experiment with peas is briefly described. In it one lot of plants 

 was grown in a complete solution, a second in the same solution but 



