572 



THE POPULAR SCIENCE MONTHLY 



periority in height of the Milwaukee chil- 

 dren is ascribed to the inferior density of 

 population and the existence of fewer urban 

 disadvantages in that city than in Boston ; 

 and the general hypothesis is drawn, from 

 Mr. Peckham's tables, that the height of 

 American-born men is more modified by the 

 conditions accompanying density than by all 

 other influences, race excepted, urban life 

 as compared with rural life tending toward 

 a decrease of stature. The rate of growth 

 of Germans appears to be considerably modi- 

 fied by residence in this country through one 

 generation; and, in intermarriage between 

 Americans and Germans, the offspring seem 

 to take the height of the taller parent. 



Use of the Gummy Secretions of Plants. 



Inquiry has often been made respecting 

 the functions of the secretory apparatus of 

 plants, or that which stores up special juices, 

 such as the resins, gums, caoutchouc, milky 

 juic83, and the waxes. Sachs, even in the 

 last edition of his botany, places these sub- 

 stances among those the office of which in 

 the economy of the plant is wholly unknown. 

 Because the secretions in question have 

 been observed to be poor in oxygen and 

 generally unassimilable, they have com- 

 monly been regarded as waste matter, use- 

 less to the organism. M. de Vries is of 

 a different opinion, and regards these sub- 

 stances as a kind of protective salve, and 

 considers them helpful in the healing of 

 wounds. Of the resin of conifers, he re- 

 marks that, if it were simply a product of 

 secretion, the accumulation of it would not 

 cause the tree to suffer. The extraction of 

 resin, however, weakens pines very consid- 

 erably, and diminishes the growth of wood 

 by about one third. Accidental wounds, 

 moreover, and even normal wounds pro- 

 duced by the fall of limbs or by splitting of 

 the bark, are very numerous in conifers. 

 Whenever a wound is produced, it is forth- 

 with covered over with a viscous and thick 

 mass of resin, which gradually hardens in 

 the air. Among non-resinous plants wounds 

 become isolated by means of a pad of heal- 

 ing tissue which sometimes covers the wound 

 completely over, but often too late to effect 

 the purpose. From this point of view, M. 

 de Vrics suggests, the conifers are superior 

 in organization to common angiospermous 



trees. The organism in coniferous trees 

 seems in a manner to have foreseen possi- 

 ble wounds, and a system of canals designed 

 solely to furnish a covering for wounds 

 seems to have been differentiated in them. 

 In a second part of his work, M. de Vries 

 treats of the function of the juices analo- 

 gous to the resins whieh are found in other 

 plants, and seeks to assimilate to the resins, 

 from different points of view, the latex, some 

 ef the gums, caoutchouc, and waxy matters, 

 lie shows that these substances also exude 

 for the occlusion of wounds, even in herba- 

 ceous plants like the northern chicories 

 and spurges, and cites some recent experi- 

 ments by M. Moll in favor of his view. It 

 would, however, be a narrow judgment to 

 conclude with him, from these experiments, 

 that the sole object of the secretions is the 

 healing of wounds. M. Raumhoff, criticis- 

 ing the work of M. de Vries, has shown 

 that the considerations on which his theory 

 rests do not furnish an adequate demonstra- 

 tion of it. It is evident, for instance, that 

 the purpose of the lactiferous tissues can 

 not be 6olely the healing of wounds, for 

 these tissues in the spurges contain starch, 

 a substance that does not assist in that of- 

 fice, and which is not a product of secretion. 

 The studies of M. Treub on the tropical 

 spurges furnish evidence that one of the 

 probable offices of their lactiferous tissues 

 is the conveyance of starch. 



Tlie Possible Annnal Yield of a Forest. 



The basis on which all sound forest man- 

 agement depends, says Colonel G. F. Pear- 

 son, is the revenue which any forest can be 

 made to pay that is to say, the income 

 which it will produce in proportion to the 

 volume of the standing trees, or, in other 

 words, its capitalized value. To this end a 

 forest should be considered as so much cap- 

 ital, represented by so many cubic feet of 

 wood ; while the amount of wood produced 

 each year, by its growth, represents the in- 

 terest thereon, and, in fact, is the revenue 

 of the forest. It is evident that it is possi- 

 ble to cut and remove every year a quantity 

 of timber equal to this annual increase of 

 wood, without diminishing the volume of 

 the standard crop. The possible annual 

 yield of a forest may be estimated on the 

 basis of a calculation that a tree, ten feet in 



