Thigmotropism of terrestrial roots. 



by 

 Frederick C. Newcombe, 



Univ. of Michigan', Ann Arbor. 



A. Introduction. 



Tlie sensitiveness of terrestrial roots to contact and pressure 

 is a subject about which little is known, but belief in which 

 seems to be widespread. Tlie fact tliat many plants in tlie trop- 

 ics use tlieir aerial roots as tendrils in elinibing lias given rise 

 to the notion tliat tliese root-tendrils like the stem-tendrils and 

 leaf-tendrils of otlier plants owe tlieir al)ility to grasp a support 

 to their sensitiveness to contact. AVlien, liowever, one exaniines 

 tlie evidence for tliigmotropism in the aerial roots of tlie lianes, 

 he must acknowledge its insufficiency. ^) Nevertlieless belief in 

 tliis thigmotropism has by the process of generalization been 

 extended froni aerial roots to terrestrial roots, though the evi- 

 dence in the latter case is scaiity iiideed. Tliis evidence rests 

 lipon but two piil)lislied observations. Of tliese publications, the 

 first is by Saclis,^) and the second by Nemec. ^) The conclu- 

 sions of Sachs liave already been disproved;"^) and Nein ec 's as- 

 siimption of thigmotropic sensitiveness in the roots of Vicia faba 

 will !)(' dcalt vvith in the following pages. 



Thü work herewith brought to publication has been carried 

 011 at intervals during several years, and represents a detailed 

 study of the thigmotropic sensitiveness of terrestrial roots. The 

 reader will be able to judge for himself whether the methods 



1) M o h 1 , Über den Bau und das Winden der Ranken und Sclüing- 

 pflanzen. Tübingen 1827; Darwin, The movements and habits of ch'mbing 

 j)lants. New York 1876, 188; Treub, Ann. du jard. bot. de Buitenzorg. III. 

 177; Went, Ann. du jard. bot. de Buitenzorg. "XII. 1; Ewart, Ann. du 

 jard. bot. de Buitenzorg. XV. 234. 



2) Sachs, Über das Wachstum der Haupt- und Nebenwurzehi. (Arbeit, 

 aus dem bot. Inst. Würzburg. I. 437.) 



''') Nemec, Über die Wahrnehmung des Schwerkraftreizes bei den 

 Pflanzen. (Jahrb. f. wiss. Botan. XXXVI. 1901. 87.) 



4) Newcombe, Sachs' angebl. thigmotr. Kurven an Wurzeln waren 

 traumatisch. (Beihft. z. Bot. Centralb. XII. 243.) 



