Ill 



Other Insectivorous Plants 49 



vascular bundles. An impulse thus travels more rapidly 

 along than across the leaf, since from the shape and lie 

 of the cells, fewer cell-walls have to be crossed in a given 

 distance. When the central glands are stimulated they 

 send some influence outwards, which reaches the external 

 tentacles and glands. There we can see one of the results 

 of its arrival in the process of aggregation which descends 

 the tentacles. 



To explain the actual mechanism of bending is a most 

 difficult problem. Various suppositions have been made. 

 Thus if w^e suppose the cells at the base of the tentacle 

 to be in a state of high water-tension and to possess great 

 elasticity, a rapid outflow of water might cause shrinkage 

 and bending. Or it may be that the living matter of cells 

 is contractile, like that of muscles. What then causes the 

 outflow, i.e. how does the stimulus set it up ? What 

 meaning, again, are we to give to the "protoplasmic con- 

 tinuity," which has been traced between the living matter 

 of cell and cell, and how far shall we grant a share in the 

 matter to the contractility of this living netAvork ? And so 

 we are face to face once more with perplexities to muse 

 over ; which, as they take form in definite questions, will 

 lead the reader towards the larger treatises and to new- 

 reflection beyond their scope in turn. 



Absorption. — It is difficult to make precise statements 

 in regard to the plant's power of absorbing the digested sub- 

 stances. Clark fed Drosera with flies soaked in chloride of 

 lithium, and after several days found that all parts of the 

 plants when burned showed the characteristic spectrum of 

 lithium. But this did not conclusively prove more than that 

 the lithium salt had been absorbed by the plant. Lawson 

 Tait, by cultivating plants with roots cut off and leaves 

 buried in pure sand watered with an ammoniacal solution, 

 showed that the sundew can not only absorb nutriment 



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