MULTICELLULAR ABSORBING HAIRS 



239 



and so produce a smooth glistening coat {Convolvulus Cneorum, 

 Plantago cylindrica, etc.). Besides helping to reduce the amount of 

 transpiration (cf. Chap. III., II., C), these distal parts of the hairs, by 

 virtue of their capillary action, retain drops of rain or dew and conduct 

 them to the basal absorbing portions. 



Two examples will serve further to explain the structure of this 

 type of absorbing hair. The leaf of Gentaurea argentea bears, on both 

 surfaces, a very dense felted covering composed of unbranched absorbing 

 hairs (Fig. 92 c). Each hair comprises an embedded basal cell, one 



Fig. 92. 



Water-absorbing hairs of various xerophytes. A. Diplotaxis Harra. B. Heliotropiwn 

 luteum. C. Centaurea argentea. D. Convolvulus Cneorum. 



to three thin-walled, slightly elongated absorbing cells, a broader and 

 somewhat thick-walled subterminal cell and a greatly elongated, air- 

 containing terminal cell, which is separated from the subterminal cell 

 by a very thick transverse wall. A wilted leaf which was immersed 

 in water except for the cut surface of the petiole was found to 

 resume its normal turgidity in the course of twenty-four hours, during 

 which period it absorbed water to the extent of 13 per cent, of its 

 weight. Both sides of the leaf of Convolvulus Cneorum are covered 

 with a shining coat of densely crowded hairs ; each hair has a very 

 thick-walled, elongated terminal cell, while the outer wall of the short 

 disc-shaped absorbing cell which intervenes between the terminal cells 

 and the embedded basal cell is exceedingly thin (Fig. 92 d). The 

 thin-walled character of the absorbing cell is rendered more striking 

 by the great thickness of the outer epidermal walls. A wilted leaf 



