CHAP. XV. 



STRUCTURE OF LEAVES. 



333 



are linear, much attenuated towards their tips, and 

 several inches in length. The upper surface is con- 

 cave, the lower convex, with a narrow channel down 

 the middle. Both surfaces, with the exception of the 

 channel, are covered with glands, supported on pedicels 

 and arranged in irregular longitudinal rows. These 

 organs I shall call tentacles, from their close resem- 

 blance to those of Drosera, though they have no power 

 of movement. Those on the same leaf differ much in 

 length. The glands also differ in size, and are of a 

 bright pink or of a purple colour; their upper sur- 

 faces are convex, and the lower flat or even concave, 

 so that they resemble miniature mushrooms in appear- 

 ance. They are formed of two (as I believe) layers 

 of delicate angular cells, enclosing eight or ten larger 

 cells with thicker, zigzag walls. Within these larger 



cells there are others marked by spiral lines, and 



apparently connected with the spiral 



vessels which run up the green multi- 

 cellular pedicels. The glands secrete 



large drops of viscid secretion. Other 



glands, having the same general 



appearance, are found on the flower- 

 peduncles and calyx. 



Besides the glands which are borne 



on longer or shorter pedicels, there 



are numerous ones, both on the upper 



and lower surfaces of the leaves, so 



small as to be scarcely visible to the 



naked eye. They are colourless and 



almost sessile, either circular or oval 



in outline ; the latter occurring chiefly 



on the backs of the leaves (fig. 14). 



Internally they have exactly the same structure as 



the larger glands which are supported on pedicels ; 



FIG. u. 



(DrosophyUum lusi- 

 tanicum.) 



Part of leaf, enlarged 

 seven times, show- 

 ing lower surface. 



