5 8 MOVEMENTS OF CURVATURE 



slowly growing tendrils as well as with those which are irritable on all sides 

 and on one side only 1 . In Fig. 18, curves representing the growth of the 

 different regions of a tendril of Pilogyne suavis are given which five minutes 

 after stimulation had curved into an arc of 5 mm. radius. Similar curves 

 were obtained by using marks placed on the sides of the tendrils to 

 determine the elongation of the convex side 2 . 



Although the exact mode of production of these changes in the rate of 

 growth is uncertain they are undoubtedly the result of the action of the 

 contact-stimulus, and this also applies to the subsequent acceleration of 

 growth in the concave side which causes the tendril to straighten after 

 temporary contact, although it is only an indirect result of the contact 

 stimulation. Fitting 3 found that the accelerations of growth and the 

 tendencies to curvature followed in the same order when curvature was 

 rendered mechanically impossible, so that a realized curvature is not 

 necessary for the production of the secondary acceleration of growth on 

 the concave side. The changes of the tissue-strains produced by the 

 attempted curvatures might, however, act as the exciting cause to the 

 secondary response, for if the tendril is kept straight the growth of 

 the convex side will tend to stretch the concave one. This is shown by 

 the fact that the tendril immediately curves when released, until the concave 

 side is slightly or not at all compressed. 



A realized curvature does, however, excite a compensating reaction 

 tending to produce straightening, as is shown by the fact that a tendril to 

 which a plastic curvature is forcibly imparted, has its growth accelerated 

 on the concave side so that it gradually straightens again 4 . 



It is evident that a chain of reactions is necessary in both radial and 

 dorsiventral tendrils, since the primary acceleration of growth occurs not 

 on the stimulated but on the non-stimulated side. Furthermore, as Fitting 5 

 found, no curvature occurs if the tendril is rubbed equally strongly on oppo- 

 site sides or around a circular zone. This applies to both radial and dorsi- 

 ventral tendrils, neither a curvature nor any acceleration of growth being 

 shown. Contact applied to the convex surface of the tendril of Strychnos 

 and of Bauhinia is, however, unable to prevent coiling around a support in 

 contact with the concave surface 6 . When the opposed stimuli produce 

 no response it is evident that they are still perceived but mutually 

 antagonize so that no reaction is awakened. The convex surface of many 



1 Trzebinski (Bull, de 1'Acad. de Cracovie, 1902, p. 123) observed that contact produced 

 disturbances in the rapidity of growth of the sporophore and sporangium of Phycomyces nitens, but 

 no details are given as to the mode of application of the contact stimulus. 



2 [These observations of Fitting's corroborate the original views of Sachs, Textbook of Botany, 



1875, P- 779-1 



3 L.c., p. 588. 4 Id., pp. 557, 582. 5 L. c., p. 582. 

 6 Ewart, Ann. du Jard. bot. de Buitenzorg, 1898, Vol. XV, pp. 208 seq. 



