728 EXPERIMENT STATION RECORD. 



It was found that on the roots of beans, peas, clovers, vetches, and others, 

 newly formed nodules were present when the plants were from three to six 

 weeks old. Perennial plants may exhibit nodules at any time when there is 

 renewed activity in the root system. The life of a nodule was found to be 

 influenced by a number of factors. In case of annual plants, when the seed is 

 ripened and the regenerative process completed, the root system ceases to grow 

 and the nodules are slowly destroyed by the nodule-forming bacteria within 

 and the saprophytic organisms without. In the case of perennial and biennial 

 plants, wlien the root system for any reason is not actively functioning, tlie 

 root tubercles are broken down in a manner similar to that mentioned above 

 for annuals. It is claimed in general that improper drainage, drought, acidity 

 of the soil, freezing, etc., interfere with the development of root tubercles, wliile 

 proper aeration, regular and sufficient watering, tlie presence in the soil of insol- 

 uble carbonates, and suitable growing temperatures encourage their formation. 



The daily march, of transpiration in a desert perennial, EorrH B. Shre\'e 

 {Caryxeyie Inni. Wafshinr/ton Pith. liiJf. {19U), pp. 6Jf, pi. 1, figs. 27; ahs in 

 Ztschr. not., 7 {1915), No. 2, pp. 122, i2.?).— This is a study of the behavior of 

 Parlinsonia microphyUa, which is said to have been selected on account of its 

 ability to overcome the adverse conditions of a largo evaporating surface (hiring 

 the entire year and a high death rate of its seedlings during the first two years. 

 The methods and details of tlie investigation are given as regards transpira- 

 tional behavior and factors correlated therewith. 



It is stated that the actual transpirational behavior of the plant is indicated 

 more accurately by measurements from small branches of trees growing in 

 the open than by those from pottetl plants, on account of the previous environ- 

 mental history of the latter. Transpirational behavior is described, this being 

 considered as indicative of physiological regulation. 



An interrelation between stomatal beJiavior and relative transpiratiou was 

 apparent. A sliglit drying out of tissues is tliought to account for some cliangi'-^ 

 ol)served to occur in this connection. 



Hourly changes in the relative transpiration rate, stomatal opening, water 

 content of leaves and twigs, and leaf temperature indicate interrelations which 

 are held to be governed by the ratio of demand to available supply of water. 



The index of foliar transpiring' power as an indicator of permanent wilt- 

 ing in plants, A. U Bakke {Hot. Gnz., 60 {1915), \o. 4, pp. 31J,-^119, fig. 1). — 

 The author has extended his previous study (E. S. R., 34, p. ^114) l>y making 

 observations on the index of foliar transpiring power of sunflower when re- 

 moved from the soil at 8.30 a. m. and allowed to wilt in the laboratory. Tlie 

 results show a steep decline for one hour, a very gentle decline during four 

 hours, and a rather sharp rise for two hours, followed by a final decline. 



The very steep initial decline Is .supposed to represent the prompt increase 

 of incipient drying within the leaves as noted by Livingston and Brown (E. S. 

 R., 27, p. 331). The gentle decline is ascribed to the period within which the 

 continuous water columns of the plant remained intact, the leaves still .slowly 

 drawing water from the stem. Tlio rise betwoiMi tlie fifth and .seventh hour is 

 considered to represent the period of the breaking of the water columns, as the 

 result of which the foliar transpiration increased on account of the removal of 

 the tensile stress and the admission of air, following which no further tensile 

 strength could be developed. After the seventh hour it is supposed that no 

 more water entered the loaves from the stem and the leaves gradually dried 

 out, showing meanwhile the decreasetl transpiring power which should accom- 

 pany desiccation. 



It appears then that the stage of wilting just previous to the rise referred to 

 represents an approach to the most intense drying possible without rupture of 



