68 



THE PRICKLES OF PLANTS. 



and in the willows of our own country. On ferns they are scattered, long, brown, 

 and entangled. 



Fig. 116. 



Fig. 117. 



Fig. 116. Two hairs from the style of a CAMPANULA, showing in a the circulation proceeding, and 

 in b emptied of its contents. The latter is not only collapsed, but retracted within itself. 



Fi?. 117. Representing the mode of growth of hairs from a single epidermal cell ; a, club-shaped; 

 6, pointed. Both from the Evening Primrose (^NOTHERA). 



The development of hairs appears to be usually a very simple process, being none 

 other than the inordinate growth of a cell of the cuticle on its free surface. Such is 

 figured by Schleiden (Fig. 11 7). 



Prickles are hard unyielding processes, with an acute and usually slightly curved 

 extremity, well fitted to hold and tear any object which may be carried against them. 

 They are very common in the rose (Rosa), and bramble (Rubus), in which plants they 

 are the growth of a single year. In other plants, as the Xanthoxylum juglandifolium, 

 they are the result of two or three years' growth. They are essentially allied to hairs, 

 since they are cellular prolongations of the cuticle, but differ greatly from them in 

 their far greater development, the rudeness of their texture, and the functions which 

 they perform. They have also a less real but a greater apparent resemblance to spines, 

 as of the sloe tree (Prunus spinosa), inasmuch as both are large and rude, and sharply 

 pointed ; but there is this essential dissimilarity viz., that the spine is a prolongation 

 of the wood of the tree (in other words, an abortive branch), whilst the latter is simply 

 connected with the cuticle or the epiphloeum of the bark of herbaceous shrubs. Their 

 use is not well known ; but they are not depositories or secretions, neither have they 

 any independent circulation. They are well adapted to enable the long and slender 

 branch to support itself by attachment to stronger plants, and also (if we may apply 

 such an expression to a mere vegetable), to enable it to defend itself from the attacks of 

 animals. They may be detached from the cutis by the force of the thumb and finger. 



Scurf has been regarded as a production analogous to hairs, inasmuch as it is a 

 cellular structure and is a process from the cutis There, however, the analogy ends, 

 and it fails in the most essential point viz., a similarity in function. It consists of 

 scales of various forms and sizes, adhering to the cutis by the whole or only a part of 



