ABSTRACTS OF REPORTS OF FOREIGN INVESTIGATIONS. 



The function of the root tubercles of leguminous plants. — A review by H. 

 W. Conn. — Tlie ruiictiou of ihe root tubt'icles Iia.s been as much discussi'd 

 as tlieir nature and structure.* At lirst they were regarded as purely 

 parasitic and therefore injurious rather than beneticial to the plant. 

 It Avas soon found, however, that they contained an unusually large 

 amount of nitrogenous inatter,f and they were for a time su|)posed to be 

 reservoirs of compounds of nitrogen. f It was next discovered that the 

 plants possessing root tubercles contained more nitrogen than those 

 without theiu, and it was thought that in some way they enable<l the 

 plants to obtain an extra amcjunt of nitrogen from the <leeper layers of 

 the soil.§ To-day it is pretty definitely proved that they have some 

 connection with the power possessed by legumes of acquiring atmos- 

 l)heric nitrogen. 



It is onl^' within recent years that plants have been known to acquire 

 nitrogen in large quantities from the air. The classical ezperimentsof 

 Boussingault, Lawes, Gilbert, and Pugh were for a time thought to 

 prove that plants do not possess this [)ower. In 1.S81, Atwater insti- 

 tuted a series ot experiments, which were repeated in 1882, and brought 

 positive evidence of the ac(juisition of large quantities of nitrogen from 

 the air by peas during their period of growth. He concluded that it 

 was extremely [)robable, though not absolutely certain, that the free 

 nitrogen of the air was thus assimilated. Later experiments revealed 

 large losses of nitrogen during germination and early growth. In the 

 accounts of these investigations it was urged that this loss of nitrogen 

 was probably caused by microbes; that it heli>ed to ex[)lain why 

 previous experimenters had failed to find proof of the acquisition of 

 atmospheric nitrogen by plants, especially legumes, but that the nega- 

 tive results obtained bj' the latter were also due to the exclusion of 

 the action of electricity or microbes, by which the assimilation of 



* For a rt^snind of rocoiit research on the nutiiro of root tiiljorcles, seo Ex|)eriiiu>nt 

 .Station Kocord, vol. ii, p. 686. 



t (le Vries, Landw., Jahrb. 6, (1877). 



t SchiHdler,.Jonr. f. Laudw.,3:? (18><5) ; Brunchorst, Bcr. d. bot. Gas ,3 (1885). 

 ^ Ward, Phil, Trans. Koy. Soc, 1887. 

 56 



