b 14 THE POPULAR SCIENCE MONTHLY. 



merging into one another, yet the type of structure, as shown by cleav- 

 age, is constant : particular kinds of, molecules severally have particu- 

 lar shapes into which they settle themselves as they aggregate. And 

 though in some cases it happens that a substance, simple or compound, 

 has two or even more forms of aggregation, yet the recognized inter- 

 pretation is, that these different forms are the forms assumed by mole- 

 cules made different in their structures by allotropic or isomeric 

 changes. So constant is the relation between the nature of any mole- 

 cules and their mode of crystallizing, that, given two kinds of mole- 

 cules which are known, from their chemical actions, to be closely allied 

 in their natures, and it is inferred with certainty that their crystals 

 will be closely allied. In brief, it may be unhesitatingly affirmed, as 

 an outcome of physics and chemistry, that throughout all phenomena 

 presented by dead matter the natures of the units necessitate certain 

 traits in the aggregates. 



This truth is again exemplified by aggregates of organic matter. 

 In the substance of each species of plant or animal, there is a proclivity 

 toward the structure which that plant or animal presents a proclivity 

 conclusively proved in cases where the conditions to the maintenance 

 of life are sufficiently simple, and where the tissue has not assumed a 

 structure too finished to permit rearrangement. The perpetually-cited 

 case of the polype, each part of which, when it is cut into several, 

 presently puts on the polype-shape, and gains structures and powers 

 like those of the original whole, illustrates this truth among animals. 

 Among plants it is well exemplified by the Begonias. Here a com- 

 plete plant grows from a fragment of a leaf stuck into the ground ; and, 

 in Begonia phyllomaniaca, complete plants grow even out of scales 

 that fall from the leaves and the stem a fact showing, like the fact 

 which the polype furnishes, that the units everywhere present have for 

 their type of aggregation the type of the organism they belong to ; 

 and reminding us of the universal fact that the units composing every 

 germ, animal or vegetal, have a proclivity toward the parental type 

 of aggregation. 



Thus, given the natures of the units, and the nature of the aggre- 

 gate they form is predetermined. I say the nature, meaning, of 

 course, the essential traits, and not including the incidental. By the 

 characters of the units are necessitated certain limits within which the 

 characters of the aggregate must fall. The circumstances attending 

 aggregation greatly modify the results ; but the truth here to be recog- 

 nized is, that these circumstances, in some cases perhaps preventing 

 aggregation altogether, in other cases impeding it, in other cases facili- 

 tating it more or less, can never give, to the aggregate, characters that 

 do not consist with the characters of the units. No favoring conditions 

 will give the laborer power to pile cannon-shot into a vertical wall ; no 

 favoring conditions will make it possible for common salt, which crys- 

 tallizes on the regular system, to crystallize, like sulphate of soda, on 



