Ill Other Insectivorous Plants 45 



tains a central mass of spirally thickened cells in immediate 

 contact with the upper ends of the conducting tracheides. 

 Around these, but separated from them by an intermediate 

 stratum of elongated cells, there is a layer of cells filled 

 with purple fluid, and outside these another somewhat 

 similar layer. These two external layers form the really 

 glandular part. Goebel insists that all the glands of 

 Droseraceas, whether borne on tentacles, as in the common 

 sundews, or quite unstalked, as in Dionsea, have essentially 

 the same structure ; the tentacled and the sessile forms 

 are connected by intermediate gradations. 



The leaves of the sundew seem to have some fascina- 

 tion for insects, but whether this is due to their colour, 

 their glittering secretion, their odour, or to all three, 

 remains uncertain. The drops are so viscid that an insect 

 may be caught if it but touch one or two of the outer 

 tentacles ; as they begin to bend and also secrete more 

 copiously the insect is carried inwards and more effectively 

 smeared. Even a large insect — such as a dragon-fly — 

 may be caught by several leaves, though in these cases it 

 is likely that the insect was to begin with in a weak state. 

 The bending of the tentacle takes place near its base, and 

 may be excited in various ways. For although the plant 

 seems to have grown accustomed to gusts of wind or drops 

 of rain, and is to its own advantage indifferent to these, 

 repeated touches will cause the tentacles to bend. On the 

 other hand, contact with any solid particle, even though 

 insoluble and of far greater minuteness than could be 

 appreciated by our sense of touch, will induce movement, 

 and one would think that in natural conditions movements 

 so induced must sometimes occur, and to no purpose. A 

 morsel of human hair, weighing only ^g^^^ of a grain, 

 and this largely supported too by the viscid secretion, 

 suffices to induce movement. Finally, the absorption of 



