ELEMENTAEY STEUCTUEE. 



57 



thickening layers, and thus collapsing when dry, so that it theR 

 resembles a more or less twisted band with thickened edges {fig. 

 132, a): while liber-cells from containing thickening material in 

 their interior, always maintain their original cylindrical forms 

 and tapering extremities {fig. 132, b). 



On young roots we find cells prolonged beyond the surface 

 which are of the nature of hairs, and have therefore been termed 

 7-adical hairs {fig. 224), The hairs which occur on the parts of 

 the flower frequently serve an indirect part in the process of fer- 

 tilization by collecting the pollen or fructifying powder which 

 falls from the stamens ; hence such are termed collecting hairs 

 {fig. 133). The collecting hairs which occur on the style of the 

 species of Campanula {fig. 134, a) are peculiar from their upper 

 end {fig. 134, V) retracting within their lower at the period of fe- 

 cundation. In some eases we find different parts of the plant 

 becoming transformed into hair-like appendages ; thus in the 

 Wig-tree {Efius Cotinus){fig. 135) the flower-stalks become con- 



Fig. 133. Fig. 134. 



Fig. 135. 



I 



Fig. 133. Pistil of Bell-flower (Campanula^, with its style 



»'J ) covered with collerting hairs. Fig. 134. Magnified repre- 



li/ sentation of two of the collecting hairs of the Bell-flower. 



kJF/ a. The hair in its norma] position. 6. The hair with the 



upper part partially drawn within its lower. FmniSchleiden. 



Fig. 135. Flowering branch of the Rhus Cotinu.<<, or Wig-tree, with 



one branch bearing fruit and the others covered with hair-like ap- 

 pendages and sterile. 



verted into hair-like prolongations, and in many cases the calyx 

 of the Composite and allied orders presents a hair\' character. 

 Such hair-like processes have, however, a different structure 

 from the hairs just described. 



2. Glands. — This name properly applies only to cells which 

 secrete a peculiar matter, but it is also vaguely given to some 

 other epidermal or sub-epidermal appendages. Glands have 

 been variously divided by authors ; thus by some, into external 



