LITERATUKE 343. 



('90), who finds additional evidence for it in the character of 

 the turnings which the two tubes from the opposite cells 

 undergo in order successfully to impinge upon each other. 



The results of experimentation upon chemotropism show 

 that various substances may direct the growth of such elon- 

 gated organs as the tendrils, roots, and hyphse of plants ; sO' 

 that greater growth takes place on the side turned from the 

 region of greatest concentration or towards it, as the case may 

 be. In many instances it can be shown that the direction of 

 growth is on the whole an advantageous one for the organism 

 — so that the directed growth may be considered an adaptive 

 one. In other cases, however, the response seems to have no 

 relation to adaptation. 



If that which controls direction is the unequal concentration 

 of chemical agents in the medium, the immediate cause is 

 excessive growth on one side, due to excessive imbibition or 

 to excessive assimilative activity. The relation between these 

 causes is doubtless complicated. The chemical agent acts 

 upon the protoplasm, changing its molecular structure ; the 

 changed protoplasm exhibits changed growth activities. Thus 

 we say the chemical agents act as stimuli. 



LITERATURE 



Aeby, J. H. '96. Beitrag zur Frage der Stickstoffernahrung der Pflanzen^ 



Landwirthsch. Versuchs-Stat. XLVI, 409-i.39. 

 AsCHOFF, C. '90. Ueber die Bedeutung des Chlors in der Pflanze. Landw. 



Jahrbucher. XVIII, 113-141. 

 Basslee, p. '87. Die Assimilation des Asparagins durch die Pflanze. 



Landwirthsch. Versuchs-Stat. XXXIII, "231-240. 

 Baumaxx, E. '95. Ueber das norinale Vorkommen von Jod im Thier- 



korper. (I. Mitth.) Zeitschr. f. physiol. Chemie. XXI, 319-330. 



28 Deo. 1895. 

 Baumann, E. and Roos, E. '96. Idem (II. Mitth.), ibidem. XXI, 481-493. 



2 Apr. 1896. 

 Baujiann, E. '96. Idem (III. Mitth.), ibidem. XXII, 1-15. 16 May, 1896.. 

 Benecke, W. '95. Die zur Ernahrung der Schimmelpilze nothwendigen 



Metalle. Jahrb. f. wiss. Bot. XXVIII, 487-530. 

 '96. Die Bedeutung des Kaliums und des Blagnesiums fUr Entwickelung 



und AA'achsthum des Aspergillus niger v. Th., sowie Einiger anderer 



Pilzformen. Bot. Ztg. LIV. 



