8o6 THE POPULAR SCIENCE MONTHLY. 



which passes off with the decline of day — the greatest intensity al- 

 ways occurring during the shedding of the pollen. Any great increase 

 of temperature is necessarily prevented by the equalizing effect of 

 evaporation from the expanded surfaces of the leaves, and the water 

 which pervades all the substances. It is only during a period of un- 

 usual energy, as in blossoming, that the heat becomes apparent. 



The light and heat set free by combustion we recognize as merely 

 the expression of chemical change and a giving back to original ele- 

 ments the forces that were stored up by vegetative activity in the 

 coal-beds of the past or in the woody fibers of later growth. In the 

 mysterious circle of Nature's means and mechanism, light, heat, and 

 chemical combination are alternately cause and effect — not, it is true, 

 in the abstract sense of cause, but, being mutually convertible or co- 

 relative, maintain necessarily reciprocal action. Now, the fact that 

 they are thus reactive and interchangeable as modes of motion offers a 

 very simple explanation of the giving out of light by plants at a mo- 

 ment when the surplus amount of thqse garnered forces is thrown off 

 during the vital processes of reproduction. 



That increased chemical activity exists at the period of flowering 

 is shown by the exhalation of an unusual amount of carbonic acid, 

 and this increased action supplies the additional heat for the elabora- 

 tion of the reproductive agents, whose preparation seems to be the 

 highest expression of energy in vegetable organization. Some doubt 

 exists as to the proximate cause of the manifestation of light by 

 flowerless or cryptogamic plants, in which are embraced the mosses, 

 fungi, etc. A study of the conditions under which it is presented 

 will, I think, enable us to refer it directly to similar chemical action. 



These plants were ingeniously named by Linnseus because the con- 

 cealed organs of reproduction offer great diversity in structural rela- 

 tions — a diversity so great that they can not even be presented under 

 one common type ; we must, therefore, look for modifications in the 

 expression of force directed by these different forms. The root-hairs 

 which form in the germination of one of the liverworts {HepaticcB) 

 have been observed to be luminous in the dim light of caverns. It 

 gathers principally upon schists, and derives its name {Schistostegd 

 Osmimdacce) from a miniature resemblance to the royal fern Osmiin- 

 da. This plant, like the true cavern-mosses, is emerald-green, and 

 develops into root, stem, and leaf. The dainty fern-like leaves or 

 fronds are of the very simplest organization, and a slender, thread- 

 like stem rises from the apex, bearing upon its summit a valvular case 

 or capsule which contains the reproductive cells or sporules. The 

 root-hairs which give out the light appear like the tangled meshes of a 

 spider's web ; and, as the same effect has been noticed in these tenu- 

 ous structures, some naturalists have attributed the appearance to re- 

 flected light. But analogy in the condition of this and other light- 

 emitting plants leads to the conclusion that it is self-luminous. 



