128 DESIGN IN NATURE 



back to lines of communication and lines of force, to the interdependency of organic and inorganic ^***®^^'^^^^^ 

 to form and movement as the outcome of hnes of communication and force in the interdependency ot ma er ^^ 

 a whole. There is a sequence of events which follow necessarily upon each other, and organic and morgamc ma 

 and vital and physical force are continually acting and reacting upon each other. ■ f 



It has long been known that the sensitive and insectivorous plants are capable of receiving impressions trom 

 without and transmitting impressions from within, and so imitating the so-called reflex nervous actions and move- 

 ments of animals. Thus, if the sensitive plant {Mimosa pudica) be touched it immediately begins to lo^'^ J^P ^^ 

 leaflets. If the contact be continued and increased, the leaf as a whole becomes depressed, and ultimately the leaf 

 stalk also These movements in response to an external impact necessarily imply two things : first, that the plant 

 feels the toucHng body, which means that the impact so produced travels into its substance from without inwards ; 

 and second, that the plant, having felt the touch or impact, generates in its substance a counter impulse which travels 

 in a direction from within outwards, and causes the movements of the leaflets, leaf, and leaf stalk referred to. No 

 other explanation, it appears to me, is possible. The plant, after a longer or shorter time, elevates its leaf stalk, 

 raises its leaf, and opens its leaflets as it were voluntarily. 





YiQ. 29. Shows the shape of the leaf of the sundew {Drosera rotundifolia) and the appearance of the tentacles when at rest and 



in action. 



A. Leaf of the sundew with its numerous long, tapering, highly sensitive hairs or tentacles, each terminating in a small oval 

 swelling, and tipped with a bleb of clear, viscid secretion very attractive to insects. Magnified four times (seen laterally). 



B. Another leaf seen from above. Magnified four times. In A and B the tentacles are not in action. 



C. In this figure a tiny speck of meat has been pliiced on the leaf, and the tentacles to the left of the spectator are seen bending 

 and pressing it in the direction of the centre of the leaf. 



D. In this figure all the tentacles are in action, due to the leaf having been immersed in a very weak solution of ammonia (one 

 part to 87,500 of water). The leaf presents the appearance witnessed when an insect is caught and conveyed to its centre by the 

 bending of the tentacles, where it is crushed and held firmly until the digestive secretion is exuded and the act of digestion, absorption, 

 and assimilation completed. The assimilation over, the tentacles gradually unbend and straighten, and prepare to receive new prey 

 (after Darwin). 



The sensitiveness and movements of the insectivorous plants are still more extraordinary. In the case of Venus's 

 fly-trap {Diov/va muscifiula) the plant is provided with an expanded, bi-lobed, hinged leaf, on the surface of which occur 

 six very highly sensitive hairs. When any insect, however minute, aUghts on or crawls along the leaf, and conies in 

 contact with the sensitive hairs, the leaf immediately folds up, closes, and captures the intruder. Nay more, it 

 crushes the insect, and exudes a secretion akin to gastric juice, with which it actually digests it. Here the double 

 lines of communication and of force become very obvious. An impulse travels inwards from the sensitive hairs to 

 the substance of the plant. This begets a counter or outward impulse, which results in the closing of the bi-lobed leaf 

 of the plant. Nor does the matter rest here : other inward and outward impulses are brought into play, whereby 

 digestion and assimilation are accomplished (Fig. 27). 



In Venus's fly-trap there is a high degree of sensitiveness, a low form of cognition, and a power to move in 

 given directions and to definite ends. 



