REASONABLENESS OF PLANTS 



It is, of course, quite impossible to explain it all exactly : 

 the sensitive part on the inside of the curve differs from the 

 outside or convex part of the tendril ; the former has a layer 

 of elongated, thin-walled cells, full of the living matter, pro- 

 toplasm, which are absent on the outer side. Immediately 

 the tendril touches the stick, the outer convex surface begins 

 to grow rapidly. It grows from forty to 200 times as fast as 

 the inner side which touches the stick ! Very soon after it 

 has clasped the stick the tendril becomes woody and forms a 

 strong, woody, spiral coil. 



These tendrils can be made to curve by a weight exceed- 

 ingly small. The most sensitive part of our own skins is 

 quite unable to distinguish so small a weight as is perceived 

 by these tendrils. Even the sensation of taste can only be 

 produced by a weight eight times as great as that shown by 

 some of them. Tendrils curve very quickly after they have 

 been touched. In twenty seconds some tendrils curve 

 {Cyclanthera\ others (Passiflora) take thirty seconds, and 

 some of them require four to five minutes or even longer 

 before they make up their minds to coil. 



Even more remarkable, however, is the fact that they do 

 not coil when raindrops fall on them, giving a much harder 

 blow than small weights. If one tendril touches or rubs 

 against another, it is said not to curve. They are persever- 

 ing little things also, for Darwin got a passion-flower tendril 

 to curve when struck or rubbed no less than twenty-one 

 times during fifty-four hours. 



If one reflects on all these curious facts, it is diflicult to 

 help feeling that these plants behave very much in the way 

 that a reasonable animal would do. There are many other 

 cases in which some vegetable does exactly what we should 

 expect of reasonable beings under the circumstances. The tip 

 X 321 



