67 



completely disappear on combustion, the organic combination volatil- 

 izing as such, or by decomposition yielding volatile products contain- 

 ing- the chlorine or sulphur.^ In evidence against this view are the 

 results obtained in the examination of the sample of Sarcohatus 

 vermictdatus, where it was found that the total amount of chlorine in 

 the plant, as determined Iw the Carius method, in which there was 

 afforded no opportunity for an}^ of the chlorine to escape, was the 

 same as the amount leached out of the ashes bj^ water, within the 

 limits of experimental error. 



Another idea that presents itself is that the bases and acids are 

 taken up by the plant in the form of salt solutions; that the plant 

 selects and retains the bases and excretes the acid radicals in some 

 manner as acids. It is noteworthy, in this connection, that it has 

 been observed generall}^ in the cases of water cultures that the nutri- 

 ent solutions gradually become acid unless special conditions are 

 introduced to prevent it. Occasionally, however, cases have been 

 found where the culture solutions actuall}^ become alkaline.^ The 

 point of special importance in this connection is that either a base or 

 an acid radical, more often the latter, is either rejected or ejected by 

 the plant. 



It seems to have been generally supposed that the acidity of these 

 solutions was duQ^to organic acids formed and excreted by the i)lant, 

 but no satisfactor}^ proof for tliis view has been adduced. The weight 

 of evidence is now decidedly against this view. It is not at all diffi- 

 cult, from the point of view of the chemist, to construct a probable 

 "mechanism " for the phenomena presented, supposing that the plant 

 has selectively retained the basic constituents and excreted the acids, 

 and that the acidity of the culture solutions is due to the free mineral 

 acids. Diels's ^ investigations in this direction are particularly interest- 

 ing. He found that certain halophilous i^lants, when placed in distilled 

 water, steadily lost the sodium chloride they contained. He showed 

 that the salt was not excreted as such,^ and offers as a probable expla- 

 nation that the greater amounts of malic acid — the formation of Avhich 

 is shown to be a usual accompaniment of growth in succulent jolants, 

 such as most of the halophytes are — decomj)oses the sodium chloride, 

 forming sodium malate and hydrochloric acid, and this latter is possi- 

 bh' excreted by the roots. ^ The solutions become acid, but, on account 

 of the experimental difficulties, it was not definitely proved that the 



' It is not intended to imply that chlorine and sulphur may not play very differ- 

 ent parts in the plant economy, but the general considerations advanced might 

 be true for either of these or other elements. 



- Witness the classical investigations of Stohmann, Sachs, and Knop, described 

 by Johnson in How Crops Grow, p. 180. 



Loc. cit. See also Kearney, Contributions from U. S. National Herbarium, 

 Vol. Y. No. 5, p. 277 (1900); and Benecke, Jahrb. fiir. wiss. Botanique. 36, 179 (1901 ). 



^This point was established as early as 1865 by Wolf, Landw. Versuchstt., 7 pp. 

 20, 211 (1865). 



^ '^ee reference to Benecke on p. 64. 



