MOVEMENTS OF IRRITATION. 501 



of which, however, need not yet be lignified, then green tissue, 

 which, however, only reaches to the epidermis here and there, 

 since there is an abundance of collenchyma. 



If we examine sections from the middle or upper part of the 

 Bryonia tendrils, the dorsiventral structure of the irritable organ 

 stands out more and more clearly. The vascular bundles are 

 crowded together in the ground tissue on the under side of the 

 tendril ; the sclerenchyma no longer forms a ring, but an arch on 

 the under side of the tendril. Similarly the collenchyma is here 

 especially abundant, while the green parenchyma constitutes the 

 bulk of the tissue on the upper side of the tendril. 



1 See Wortmann, Botan. Zeitung, 1887, No. 7. 



2 See Pfeffer, Untersuchungen aus d. lot. Inst. zu Tubingen, Bd. 1, p. 483. 



3 See H. de Vries, Arbeiten des botan. Inst. in Wurzburg, Bd. 1, p. 302, and 

 Landwirthschl. Jahrb., Bd. 9, p. 511. 



4 See 0. Miiller, in Conn's Beitrdge zur Biologic der Pflanzen, Bd. 4, p. 120. 



191. Experiments with Tendrils of the Ampelideae. 



The branched tendrils of Vitis vinifera are not nearly so sensi- 

 tive as those of Sicyos and Cyclanthera discussed in 190. These 

 latter, under favourable circumstances, react almost instantane- 

 ously and very energetically to the stimulus of contact. Vitis 

 tendrils, even after strong stimulation, curve only slowly. I 

 found on one occasion that a branch of a Vitis tendril which had 

 been drawn several times between the fingers, was distinctly 

 curved, at a high summer temperature, at the end of twenty 

 minutes. In all other cases, especially when the temperature was 

 not so high, the effect of the stimulus was not clearly observable 

 for an hour or two. When a tendril of Vitis has curved owing to 

 transitory stimulations, it slowly straightens again, and is then 

 once more irritable. If we place a thin wooden rod near a Vitis 

 tendril, to serve as a support, the tendril can readily coil round it. 

 The free part of the tendril, between the support and the plant, 

 draws itself together corkscrew-fashion; but this takes place 

 slowly, often not till a few days have elapsed. 



The tendrils of Ampelopsis quinquefolia (wild vine) behave in a 

 very characteristic manner. Such a tendril is depicted in Fig. 167 ; 

 it has not yet made any attachment. The tendril branches are 

 only capable of winding in certain individuals ; they are mostly 



