424 



THE POPULAR SCIENCE MONTHLY. 



of heat. 'Mr. Wallace, defending his view, 

 says that, " if the white coloration of the 

 Arctic animals stood alone, it might be 

 thought necessary to supplement the pro- 

 tective theory by some physical explanation, 

 but we have to take account of the parallel 

 cases of the sand-colored desert animals, 

 and the green-colored denizens of the ever- 

 verdant tropical forests ; and, though in 

 both these regions there are numerous ex- 

 ceptional cases, we can almost always see 

 the reason of these, either in the absence of 

 the need of protection, or in the greater im- 

 portance of conspicuous covering. In the 

 Arctic regions the exceptions are particu- 

 larly instructive, because in almost every 

 case the reason of them is obvious." The 

 Arctic wolf does not turn white, because he 

 hunts in packs, and concealment is not ne- 

 cessary ; the musk-sheep, yak, moose, cari- 

 bou, and reindeer are able to take care of 

 themselves, and need no protection or con- 

 cealment. The glutton and sable are dark- 

 colored because they live in trees, and must 

 look like them. The raven, living on car- 

 rion, requires no concealment, and continues 

 black. Mr. Wallace is of the opinion that 

 color has very little to do with the absorp- 

 tion or radiation of heat, because those mat- 

 ters are largely determined by the struct- 

 ure and surface-texture of the colored sub- 

 stances. 



A Mystery of the Growth of Trees ex- 

 plained. Mr. John T. Campbell relates in 

 the "American Naturalist" his discovery of 

 one of the causes of the phenomenon of 

 particular tracts of land being covered with 

 a simultaneous, nearly exclusive, growth of 

 trees of a particular species. Some have 

 ascribed the phenomenon to a peculiar fit- 

 ness of the soil to particular kinds of vege- 

 tation, which he does not find to exist. His 

 own explanation is very simple, and is to 

 the effect that the matter lies wholly or 

 mainly in the fact of the ground being in a 

 fit condition to receive the seeds of the va- 

 rious species when they fall upon it. Seeds 

 of different kinds fall at various seasons, 

 and when the ground is in various condi- 

 tions as to moisture, etc. Those that find 

 the ground in good condition sprout and 

 grow, if no accident occurs to remove the 

 plants when very young. Mr. Campbell has 



tested this view in his surveys in the occa- 

 sionally flooded bottom-lands of the Wa- 

 bash River, and illustrates it by following 

 the futures of the seeds of three species 

 of trees. The balls of the sycamore or but- 

 ton-wood begin falling early in the spring 

 months, and, if a flood is receding at the 

 time, they stick to the soft, moist banks 

 wherever they touch them, and particularly 

 along the highest parts of the sand-bars. 

 Were it not for the subsequent floods in the 

 same spring, no other trees could grow, for 

 these would occupy the ground. But they 

 are easily killed during their infancy by 

 overflows, and this is what happens to most 

 of them. The Cottonwood is the next in or- 

 der of shedding seed, and, if another flood 

 is receding while this is taking place, it will 

 have killed all the sycamores which it has 

 covered, and sprout the cottonwoods. These 

 in turn may be killed by the next flood. It 

 is the turn of the maples next to shed their 

 seed, and try for the ground. If either of 

 these species succeeds in making wood with- 

 out a flood, it will hold the ground, and its 

 rivals will not be able to get a place. Last 

 spring the edge3 of the successive planta- 

 tions escaped the next floods after the seeds 

 fell upon them, and Mr. Campbell could see 

 along the river-banks three belts of young 

 trees, and distinguish them by their gen- 

 eral appearance. The upper belt was of 

 sycamore, the second (downward) of Cot- 

 tonwood, and the third of soft maple. In 

 June a bigger flood came than any that 

 caused the seeds to sprout, and killed all 

 the young trees. 



Water-Melon Sirnp. In response to 

 the inquiry by Dr. H. Carrington Bolton 

 concerning the manufacture of sugar from 

 water-melons (see June number, page 287), 

 Mr. E. A. Gastman, of Decatur, Illinois, writes 

 as follows: "About 1842 the manufacture 

 of molasses was carried on here in Central 

 Illinois from melons. I do not know how 

 extensive nor how successful it was, but I 

 remember very clearly when a boy on the 

 prairies near Bloomington that our neigh- 

 bors frequently raised large crops of water- 

 melons, from which they made molasses." 

 It will be observed that the extract from 

 Boyle's work communicated by Dr. Bolton 

 mentions a " sirup," not sugar. 



