ABSORPTION-CELLS ON LEAVES. 



239 



this is the case, teeth of the kind are found on this narrow green ridge which runs 

 along the groove. In Telekia, a handsome herbaceous plant of wide distribution in 

 the south-east of Europe, these teeth — conical or club-shaped— springing from the 

 margin of the petiole-groove are incurved, and are in general so placed that their 

 blunt apices project into the groove. But precisely on these obtuse tips of the 

 teeth are situated cells with very thin outer walls easily permeable to water, and 

 having contents with a strong attraction for it. Thus, as soon as the groove of the 



Fig. 56.— Water-receptacles. 

 ■ In a Teasel. Dipsacus laciniatus. 2 In the American Silphium per/oliatum. 



petiole is filled with rain, collected from the surface of the leaf, the tips of the 

 conical teeth are moistened, and they suck up the water. 



Lastly, we have to mention the curious receptacles appertaining to foliage- 

 leaves in which water from the atmosphere accumulates and continues to stand for 

 weeks without being protected from evaporation by the excretion of special 

 substances. Any region or portion of the leaf may participate in their construction. 

 In Saxlfraga peltata the lamina is shaped like a shield and forms a shallow plate 

 with the concave surface turned to the sky. In the Cloud-berry (Rubus Chamce- 

 morus) the formation of basins is brought about by the margins of the reniform 

 lamina being superimposed over one another as if to make a spathe. In the various 

 species of Winter-green, especially in Pyrola unijlora, the pale cauline leaves, 



