Direction of Thorns and Prickles. 7 1 



so excessively numerous and so well known, that I 

 may spare myself the trouble of giving a more de- 

 tailed account of them. There are, however, two 

 points which I must touch on, at least in a cursory 

 manner. 



While spines (modified branches), as a rule, either 

 stand out horizontally or have their points directed 

 upwards, and thus evidently protect the leaves behind 

 them from wholesale destruction by the larger browsing 

 animals, the prickles and sharp bristles on the axis 

 usually point downwards, so as to present a threatening 

 front to all animals that might wish to crawl up the 

 stem. Even leaf-prickles will be found to have in part 

 a similar arrangement ; and an examination of thistle- 

 heads will show at once that the prickles on the invo- 

 lucrum, at least on its lower bracts (see, for instance, 

 the capitulum of Carlina vulgaris L., Plate I. fig. 20), 

 point downwards. I have also noticed that not un- 

 frequently these down-pointing needles are massed at 

 certain spots. The most frequent spot is the upper 

 end of the internode, where the leaves are given off, 

 and where such an arrangement is the more feasible, 

 because it is at this place that the prickles and bristles 

 which shoot out from the epiderm of the stem inter- 

 mingle with those which proceed from the leaf-bases. 

 This may be noticed, for instance, in many Asperifolise, 

 Labiatse, and Dipsacese, and may be especially well 

 seen in Galeopsis grandiflora, pubescens, Tetrahit, and 



