PROTECTIVE ARRANGEMENTS ON THE EPIDERMIS. 321 



daughter-cells; the division is repeated and gives rise to a small chain of three, four, 

 or five short cells which project slightly above the surface of the leaf. The top cell 

 does not divide further, but enlarges in a striking manner, not, oddly enough, 

 lengthening in an upward direction, but transversely, parallel to the leaf-surface] 

 forming a lancet-shaped, rod-like structure, which shades the leaf, and is supported 

 by its sister cells as if on a pedestal. Thousands of such curious hair-structures, 



Fig. 77. Covering Hairs. 



1 Articulated woolly hairs of Gnaphalium Leontopodium. 2 Articulated velvety hairs of Gloxinia speciosa. Silky hairs of 

 Convolvulus Cneorum. * Ribbon-like flattened woolly hairs of Gnaphalium tomentosum. Spiral woolly hairs of Cen- 

 taur 'ea Ragusina. Stellate hairs of Alyssum Wierzbickii. f Umbrella-shaped hairs of Koniga spinosa; surface view. 

 Vertical section of the same hairs. Stellate hairs of Draba Thomasii. x about 60. 



which may best be compared to compass-needles, clothe the surface of the leaf in 

 close proximity to each other, and when they are arranged in a regular manner, 

 they reflect the light uniformly, and produce a distinctly silky lustre. If they are 

 twisted, this lustre is lessened to a greater or less extent. This variety of hairs, 

 called T-shaped, is distributed in a remarkable way. Numerous species of Astra- 

 galus, the scabious of the Mediterranean flora (Scabiosa cretica, hymellia, gramini- 

 folia), several Crucifers (Syrenia, Erysimum), native on the steppes of Southern 

 Russia, the magnificent Aster argophyllus of Australia, and particularly numerous 



VOL. L 21 



