4 8o THE POPULAR SCIENCE MONTHLY. 



the later years they gradually dry and wither ; still, under these cir- 

 cumstances they naturally require special protection. They are, as a 

 general rule, tough, and even leathery. In many species, again, as is 

 the case with our holly, they are spinose. This serves as a protection 

 from browsing animals ; and in this way we can, I think, explain the 

 curious fact that, while young hollies have spiny leaves, those of older 

 trees, which are out of the reach of browsing animals, tend to become 

 quite unarmed. 



In confirmation of this I may also adduce the fact that while in the 

 evergreen-oak the leaves on well-grown trees are entire and smooth- 

 edged like those of the laurel, specimens which are cropped and kept 

 low form scrubby brushes with hard prickly leaves.* 



Mr. Grindon, in his " Echoes on Plant and Flower Life " (p. 30), 

 says that "the occurrence of prickles only here and there among plants 

 shows them to be unconnected with any general and ruling require- 

 ment of vegetation. We can only fall back upon the principle laid 

 down at the outset, that they are illustrations of the unity of design in 

 Nature, leading us away from the earth to Him who is ' the end of 

 problems and the font of certainties.' " Surely, however, it is obvious 

 that the existence of spines and prickles serves as a protection. 



Another point of much importance in the economy of leaves is the 

 presence or absence of hairs. I have already observed that most ever- 

 greens are glossy and smooth, and have suggested that this may be an 

 advantage, as tending to prevent the adherence of snow, which might 

 otherwise accumulate and break them down. 



The hairs which occur on so many leaves are of several different 

 types. Thus, leaves are called silky when clothed with long, even, 

 shining hairs (silver- weed) ; pubescent or downy, when they are 

 clothed with soft, short hairs (strawberry) ; pilose, when the hairs are 

 long and scattered (herb-robert) ; villous, when the hairs are rather 

 long, soft, white, and close (forget-me-not) ; hirsute, when the hairs 

 are long and numerous (rose-campion) ; hispid, when they are erect 

 and stiff (borage) ; setose, when they are long, spreading, and bristly 

 (poppy) ; tomentose, when they are rather short, soft, and matted ; 

 woolly, when long, appressed, curly, but not matted (corn-centaury) ; 

 velvety, when the pubescence is short and soft to the touch (fox- 

 glove) ; cobwebby, when the hairs are long, very fine, and interlaced 

 like a cobweb (thistle, cobwebby houseleek). The arrangement of 

 the hairs is also interesting. In some plants there is a double row of 

 hairs along the stem. In the chickweed only one. This, perhaps, 

 serves to collect rain and dew, and it is significant that the row of 

 hairs is always opposite to the flower-stalk, which also has a single 

 row. Now, the flower-stalk is for a considerable part of its life turned 

 downward, with the row of hair outward. This, perhaps, may ac- 

 count for the absence of hairs on that side of the stem. 

 * Bunbury, " Botanical Fragments," p. 320. 



