THE THORN'S OF PLANTS. 501 



of the thorns in moist air was effected in two different ways. The 

 thorns, when they possess the morphological significance of a 

 limb of the plant, whether of a leaf, as in Berberis, or a bough, as 

 in Ulex, have a tendency in the saturated air to return to the nor- 

 mal type. When they proceed from organs that are not indis- 

 pensable to the life of the plant, whether from a stipule as in 

 Eohi7iia, or from a stipule peduncle as in Xanthium, they tend 

 constantly to disappear by retrogression. 



The influence of light on the production of thorns was studied 

 by M. Lothelier in a similar manner. His results were for the 

 most part parallel. Shade tends to suppress the thorny parts of 

 plants. The tendency is exhibited sometimes in a return to the 

 normal form of the organ ; but more frequently the thorns suffer 

 a greater or less atrophy in the shade. 



It is evident, then, that the conditions that most influence the 

 production of thorns are especially dryness of thq air and inten- 

 sity of light. There are also, doubtless, other conditions of life 

 that act in the same direction. I recollect having seen a culti- 

 vated and a wild olive tree growing side by side in the south. 

 Only the latter had thorns. This even seems to me to be a gen- 

 eral law which M. Lothelier has unfortunately not touched upon 

 that wild plants lose their thorns when they have been cultivated 

 for several generations. It seems as if the plant, when brought 

 under the protection of man, gradually gives up its defensive 

 arms, which are thenceforward not needed, since its enemies are 

 kept away by the care of its master. 



The ofiice of thorns is not limited to defending plants against 

 herbivorous animals. With a number of plants, particularly 

 those which form long shoots and live in thickets, thorns, usually 

 curved downward, help hold up the stems. When thorns are 

 localized on flowers, fruits, and seeds there seems generally to be 

 a purpose of aiding in the dissemination of the seeds by enabling 

 them to hook themselves in the fleeces of animals that come to 

 graze among them. The thorns then serve for the defense of the 

 species rather than of the individuals. The seeds which are aided 

 by this mode of dissemination are called zoophiles, while those 

 which are adapted to dissemination by the wind are called anemo- 

 philes. Translated for The Popular Science Monthly from La 

 ^Nature. 



Dean Bitckland's interest in hyenas, whose remains and the remains of their 

 feasts he found in the Kirkdale Cavern, caused some amusement to Lyell, who is 

 quoted in Mrs. Gordon's Life of Buckland as writing to Mantell in 1826 : " Buck- 

 land has got a letter from India about modern hyenas, whose manners, habita- 

 tions, diet, etc., are everything he could wish, and as much as could be expected 

 had they attended regularly this course of his lectures." 



