GENERAL VIEW 391 



in hydrochloric acid gives off fumes when introduced into a bell-jar in which the 

 plants have been kept. This substance, according to Wicke, is Trimethylamine ' in 

 the case of Chenopodium. Mould-fungi when grown in an alkaline solution excrete 

 ammonia in abundance 2 , and the same thing commonly occurs during putrefaction, 

 while the evolution of ammonia noticed by certain authors from germinating seeds 

 and from agarics was apparently due to the decomposition of dead parts 3 . Loseke 

 states that Agaricus oreades evolves prussic acid but apparently only after death, 

 and the same thing occurs on the death of plants containing amygdalin, such as 

 Pangium edule 4 . 



Plants can continue to grow slowly for a time and produce new leaves, 

 shoots, &c., even when the supply of nitrogen is deficient or ceases, for the 

 younger organs are able to withdraw a certain amount of combined nitrogen 

 from the older ones 5 . Boussingault found that a plant of Helianthus 

 argophyllus increased its dry weight 4-6 times without being supplied with 

 nitrogen ; but a similar plant supplied with potassium nitrate acquired 

 a dry weight 188 times greater than that of the seed. Even a small 

 supply of nitrogen causes a marked increase in the dry weight. It is very 

 difficult to keep a nutrient solution free from all combined nitrogen, and 

 a fungus is able to extract every trace present in the culture fluid, and can 

 also utilize any traces of ammonia conveyed to it by the air. 



When all the other conditions are normal, but only a minimum amount 

 of combined nitrogen is present, any addition of the latter will produce 

 a correspondingly increased growth, and a certain proportionality has often 

 been observed between the two 6 , although it is not surprising that the 

 relationship is not always a direct one, and that in some cases none can 

 be observed. 



The circulation of nitrogen. It has already been shown how the specific 

 peculiarities of different organisms are such as to maintain a continual circulation 

 of nitrogen, and to ensure the maintenance of an approximate balance in the 

 organic world between the loss and gain of combined nitrogen (cf. Sect. 51). 



1 Wicke, Bot. Zeitung, 1862, p. 393 ; Chevalier, Ann. d. sci. nat., 1824, T. I, p. 444. 



2 According to Reinke (Unters. a. d. Bot. Lab. in Gottingen, iSSi, Heft 2, p. 9) Aethalium 

 septicum produces ammonia. 



3 Cf. Wolff u. Zimmermann, Bot. Zeitung, 1871, p. 280. Seeds: Hosaeus, Jahresb. d. Agr.- 

 Chem., 1867, p. 100 ; Rauwenhoff, Linnaea, 1859-60, Bd. XXX, p. 219. M. Schultz (Journ. f. prakt. 

 Chem., 1862, Bd. LXXXVII, p. 129) states that nitrogen is also formed. 



* Agarictis: Loseke, Chem. Centralbl., 1871, p. 520. Pangium: Treub, Ann. d. jard. hot. 

 d. Buitenzorg, 1895, T. xm, p. I. 



5 Cf. Hellriegel, Unters. iiber d. Stickstoffnahrung, iSSS, pp. 19, 174. The same occurs when 

 the supply of phosphorus is scanty. 



6 Boussingault, Agronomic, &c., 1860, T. I, p. 233; Hellriegel, Jahresb. d. Agr.-Chem., 

 1868-9, P- 2 47> an ^ Unters. iiber d. Stickstoffnahrung, iSSS, pp. 55, &c. ; Ritthausen, Versuchsst, 

 1873, Bd. XVI, p. 384 ; Fittbogen, Landw. Jahrb., 1874, P- J 4^ > E. Wolff, Versuchsst, 1877, Bd. xx, 

 P- 395- 



