284 Remarks on the Structure of Wood. [May, 



may tlserefore prove to be identical with the P. humicola of Otho 

 Fabricius (Fauna Groenlandica,) of which we are unable to refer 

 to any but short and unsatisfactory descriptions, which do not co- 

 incide well with our insect. 



This is an abundant species in our forests in the winter and fore 

 part of spring. At any time in the winter, whenever a few days 

 of mild weather occur, the surface of the snow, often, over whole 

 acres of woodland, may be found sprinkled more or less thickly 

 with these minute fleas, looking, at first sight, as though gunpow- 

 der had been there scattered. Hollows and holes in the snow, out 

 of which the insects are unable to throw themselves readily, are ot- 

 ten black witjj the multitudes which here become imprisoned. 

 The fine meal-like powder with which their bodies are coated, 

 enables them to float buoyantly upon the surface of water, without 

 becoming w^et. When the snow is melting so as to produce small 

 rivulets coursing along the tracks of the lumberman's sleigh, these 

 snow-fleas are often observed, floating passively in its current, in 

 such numbers as to form continuous strings; whilst the eddies and 

 still pools gather them in such myriads as to wholly hide the ele- 

 ment beneath them. 



REMARKS ON THE STRUCTURE OF WOOD. 



Illustrated by a Plate. 

 BY E. EMMONS. 



Structure in organized as well as unorganized beings furnishes 

 the most certain and reliable criteria for recognizing the families 

 to which they belong. The minute and anatomical structure of 

 the teeth of fish and quadrupeds may always be employed as a 

 means for distinguishing the genera and species. Structure too, 

 in unorganized bodies is equally characteristic. The law of at- 

 traction, or the electric force so called imparts regularity to the 

 movements of the atoms as they approach each other; and hence, 

 the component particles of the same substance are always arranged 

 in the same manner. The body produced is built up by regular 

 and as it were concerted movements of its molecules, there is 

 therefore, not only a regular external form, but also a regular ar- 

 rangement of the interior. Such bodies are termed chrystals. 

 A physical law governs the arrangement of all the atoms which 

 enter into their composition, and though the perfection of the ar- 

 rangement may depend upon external circumstances, still the 

 force itself is never absent. 



The law of structure, however, as it appears in organized bo- 

 dies is quite different. It is a force which belongs solely to living 



