648 THE POPULAR SCIENCE MONTHLY. 



There can be little doubt on this latter point. I think we may cer- 

 tainly say that the earliest form which existed was a twining plant. 

 We see that twining plants do not possess the essential feature of leaf- 

 or tendril-bearers, namely, the sensitiveness to a touch which enables 

 a leaf or tendril to grasp a stick. But, on the other hand, most leaf- 

 and tendril- climbers do possess the essential quality of a twiner the 

 power of revolving or swinging round, which exists in the shoots, 

 leaves, or tendrils of so many of them. This power of revolving merely 

 serves in some leaf- and tendril-climbers to carry on the search for 

 supports ; but other leaf- and tendril-climbers, as we have seen, do 

 actually wind spirally round a stick exactly like a true twiner. How 

 twiners originally obtained their power of swinging round we need not 

 now inquire ; it seems to be merely an increase of a similar movement 

 which is found to occur in a meaningless manner in other plants. Thus 

 several flower-stems have been observed bowing themselves over and 

 swinging round in small circles, like climbing plants. Here the move- 

 ment is merely an unintelligible concomitant of growth, for, as we see, 

 the movement is of no advantage to the flower-stem. But the exist- 

 ence of this movement is of great interest to us, for it shows how a 

 twining plant might be developed by a similar movement being found 

 to be advantageous, and being increased by natural selection to the 

 requisite extent. 



Another question which may occur to us is this : In what way is 

 climbing by leaves or tendrils a more perfect method than twining ? 

 Why, when a plant had become a twining plant, did it not rest satis- 

 fied ? The fact that leaf- and tendril-climbers have been developed 

 out of twiners, and not vice versa, is a proof that climbing by leaves 

 or tendrils is a more advantageous habit than twining ; but we do not 

 see why it should be so. If we inquire why any plant has become a 

 climber, we shall see the reason. Light is a necessity for all green 

 plants ; and a plant which can climb is enabled to escape from the 

 shadow of other plants with a far less waste of material than a forest- 

 tree, which only pushes its bi'anches into the light by sheer growth. 

 Thus the weak, straggling stem of a climbing plant gets all the advan- 

 tages gained by the solid, column-like tree-trunk. If we apply this 

 test which is the most economical plan of climbing, twining, or leaf- 

 climbing Ave see at once that a plant which climbs by seizing wastes 

 far less material than one which twines. Thus a kidney-bean, which 

 had climbed up a stick to a height of two feet, when unwound from its 

 support was found to be three feet in length, whereas a pea which had 

 climbed up two feet by its tendrils was hardly longer than the height 

 reached. Thus the bean had wasted considerably more material by its 

 method of climbing by twining round a stick, instead of going straight 

 up, supported by its tendrils, like the pea. There are several other 

 ways in which climbing by tendrils is a much better plan than twining. 

 It is a safer method, as any one may convince himself by comparing 



