498 THE POPULAR SCIENCE MONTHLY. 



surveys, wherever such co-operation will advance the work of the 

 survey in accordance with its general scope and plans and will 

 assist the local surveys. 



The division of engraving and printing has been very suc- 

 cessful in its work on the geologic folios; and it is hoped that 

 arrangements can be perfected and authority secured for engrav- 

 ing and printing under its immediate direction all the maps of 

 the survey. 



Such special studies will be made in the chemical, paleonto- 

 logical, petrographical, and physical laboratories as may be need- 

 ful to solve the problems that arise in connection with the areal 

 geology or in the investigation of important scientific and eco- 

 nomic problems. 



The legislative branch of the Government has been very liberal 

 in the past, and it is anticipated that the work will be fully sus- 

 tained in the future. On the part of the survey it is proposed to 

 retain the services of the most capable men that can be secured ; 

 to maintain the work at the highest standard of efficiency possible ; 

 and to advance it as rapidly as the means provided will permit. 



THE THORNS OF PLANTS. 



By M. HENEI COUPIN. 



THE seeming absence of means of defense in plants, putting 

 them in contrast to the eye with animals, which are boun- 

 tifully and variously armed, is only apparent. A not very close 

 examination of the behavior of plants toward animals, their great 

 enemies, will soon satisfy one that they have many protective 

 organs, some of them very efficacious. The spines, thorns, and 

 prickles with which the stems and the leaves of some plants 

 bristle are known to all, and we can hardly fail to perceive a 

 protecting function in the aggressive defense of plants against 

 animals and against the hand of man put forth to pluck them. In 

 the spring, for instance, when vegetation is very little forward, 

 the plum trees would soon disappear completely under the attacks 

 of cattle, sheep, horses, and other foliage-loving animals, if Nature 

 had not provided them with those long, sharj) spines that make 

 browsing of them very difficult if not impossible. The shapes of 

 thorns are various, but may always be brought back to a protu- 

 berance broad at the base and pointed at its free end, and of an 

 extremely hard consistence. Usually simple, they are sometimes 

 bifid or trifid. Their positions are various. All the organs of 

 plants may be said to bear them : the stem, as in the rose ; the 

 base of the leaves, as in the barberry ; the leaves, as in the thistle ; 



