496 PHYSIOLOGY OF GROWTH. 



torsion has therefore developed, as may very frequently be 

 observed in twining stems. The origin of this torsion is most 

 intimately bound up with the development of the free turns of 

 our stem. When the turns by straightening of the stem dis- 

 appear, they are converted into a homodromous torsion, i.e. a 

 torsion corresponding in direction with, the winding of the plant. 1 



1 The more recent researches on twining plants will be found especially in 

 the following treatises : H. de Vries, Arbeiten d. botan. Inst. in Wilrzburg, Bd. 

 1 ; Schwendener, Monatsberichte d. Berliner Akad., 1881, December ; Ambronn, 

 Bericlite d. Sachsischen Gesellsch. d. Wissensch. ; Wortmann, Botan. Zeitung, 

 1886. The results of my investigations respecting twining plants agree in all 

 essential points with those of Sachs and Wortmann. 



190. Experiments on the Tendrils of the Cucurbitaceae. 



There are many plants, belonging to very different families, 

 which are furnished with tendrils. These thread-like organs are of 

 service to the plants in climbing. They are able to attach them- 

 selves to supports, and so prevent the plants from falling. 



To familiarise ourselves with the remarkable peculiarities of 

 tendrils, it is very convenient to employ for examination a series of 

 Cucurbitacere, especially Cyclanthera explodens and Sicyos angu- 

 latus. The former we grow in not too small flower-pots, the latter 

 in the open ground. Both are raised from seeds.* When the 

 plants have reached a certain size, it is necessary to furnish them 

 with supports for the tendrils to fix themselves to. 



If we examine a vigorously developed specimen of Cyclanthera 

 explodens, it is seen that the tendrils not yet fixed to supports, and 

 straight, are constantly in a state of movement. They are carried 

 round in space in a circle, a fact which is really due to the rotat- 

 ing nutation of the shoot carrying them. I observed a tendril of 

 Cyclanthera perform a complete revolution, at a high summer 

 temperature (over 20 C.), in the course of an hour. But in many 

 plants not only the tendril-bearing shoots, but also the tendrils 

 themselves, are capable of performing rotating nutation. 1 These 

 movements exhibit themselves in a pure form when we exclude the 

 shoot nutations by fixing the shoots to a stick at the point of in- 

 serbion of the tendrils. The biological importance of the nutations 

 is very considerable. The growing tendrils are thereby carried 



* The Sicyos plants are first cultivated in flower-pots, and then, when they 

 have attained a sufficient size, transplanted. 



