LINES OF COMMUNICATION AND FORCE 



129 



In the sundew (Drosera rotundifolia) the arrangements are, in some senses, even more complex and astounding 

 (Figs. 29 and 30). 



In this extraordinary plant, the expanded leaf is studded with a very large number (200 or so) of amazingly 

 sensitive hairs or tentacles, and the tips of these tentacles, marvellous to relate, are each provided with a speck of 

 glistening viscid secretion which is very attractive to insects. The trap in this case is not only set but baited. 



When an insect touches one or more of the numerous tentacles, the viscid secretion clogs the wings and feet of 

 the insect, and makes escape difficult, and, in most cases, impossible. This is the first stage of capture. No sooner 

 is the insect entangled than the sensitive hairs or tentacles all around begin to inflect ; the inflection is continued 

 until by a progi;essive rolling movement the insect is carried to the centre of the leaf, where it is firmly pinned down. 

 This is the second stage of capture. The third consists in the crushing of the insect against the surface of the leaf 

 by the infolded tentacles and the exudation of an acid secretion resembling the gastric juice of the human stomach. 

 The insect caught and crushed is finally digested and assimilated. Digestion and assimilation having been accom- 

 phshed, the sensitive tentacles unbend and become straight as at first, each in due course being provided at its 

 tip with a tiny drop of glistening secretion calculated to entice and ensnare other insects of all kinds, from small 

 beetles to even butterflies and dragon flies. The mechanism employed by the sundew to catch and devour insects 

 is, in some respects, highly complex. It certainly involves lines of communication and of force, but is not a reflex 

 act in the ordinary sense ; the latter requiring an elaborate nervous mechanism. 



■f/'M:A.TK-fi 



Fig. 30. — Shows the clouding or staining of the leaf of the sundew during digestion (magnified twice). 



A. Appearance presented by the leaf before feeding. 



B. The same leaf five minutes after a small portion of dry proto-albuminose had been placed on it. The clouding or dark stain 

 represents the position of the proto-albuminose ; some of the tentacles are seen bending towards it. 



C. The same leaf twenty-eight minutes after feeding. The proto-albuminose is partly dissolved, and the clouding or staining 

 occasioned is spreading over the leaf and down the leaf stalk. More of the tentacles are also bent. 



D. The same leaf twenty-eight hours after feeding. The proto-albuminose is now largely dissolved, and the area of the clouding 

 or staining of the leaf and leaf stalk greatly enlarged. Absorption is evidently occurring. The number of tentacles bent is also 

 increased (after Gillespie). 



First, there is the touch or impact of the insect against the sensitive hairs ; second, the inflection or bending of 

 the individual hairs touched ; third, a combined inflection and rolling movement of other hairs whereby the insect 

 is carried to the centre of the leaf ; fourth, the crushing of the insect on the centre of the leaf ; fifth, the exudation 

 of a substance analogous to gastric juice, and the digestion and assimilation of the insect. Finally, there is the 

 unbending or straightening of the tentacles and the supplying afresh of their tips with what is practically a tempting 

 bait with a view to fresh captures of insects. These arrangements plainly necessitate sensitiveness and doable lines 

 of communication and of force. The plant feels, and, within limits, knows when the insect touches it. This impfies 

 an impulse travelhng from without inwards, that is, from the insect into the substance of the plant. The 

 tentacles bend not at their tips but at their base, and digestive secretion is poured forth ; which means counter 

 impulses which travel from within outwards. The unbending movement of the tentacles is also occasioned by an 

 impulse travelling from within outwards. This follows, because it is quite evident that the tentacles which are 

 made to bend by one impulse or force cannot be made to unbend by the same impulse or force. They are counter 

 movements, and must be produced by coimter impulses or forces and counter fines of communication. 



The co-ordinated, purpose-fike, semi-intelfigent movements and acts of the insectivorous plants can only be 

 explained either by the direct interposition of a First Cause, or by assigning to them powers not dissimilar and in 

 some respects not inferior to those exercised by many animals, 



VOL. I. ^ 



