PROTECTIVE AIUIANGEMENTS 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 fm-ther, 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, 







g!/^f% 





Fig. 77.— Covering Hairs. 



I Articulated wuully hairs of GnaphalUnn Lemitopudinm. " Articulated velvety hairs of Gloxinia speciosa. 3 silky hairs of 

 Convolvtthis Cncoruia. ■* Ribbou-Iike flattened woolly hairs of Gnaphalium tomentosum. s Spiral woolly hairs of Cen- 

 taitrea liaijttiiina. 6 Stellate hairs of Alystmiit Wüizhirkü. ? Umbrella-shaped hairs of Eoniga npinosa; surface view. 

 8 Vertical section of the same hairs. * .Stellate hairs of Draba Thomasii. x about 50. 



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 ai-e 

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

 called T-shaped, is distributed in a remai'kable way. Numerous species of Astra- 

 galus, the .scabious of the Mediteri'anean flora (Scabiosa cretica, hymeltia, gramini- 

 foliii), several Crucifers (Syrenia, Eryshuum), native on the steppes of Southern 

 Russia, the magnificent Aster ai'gophylliis of Australia, and particularly numei-ous 



Vol. I. 21 



