1901.] NATURAL SCIENCES OF PHILADELPHIA. 455 



spliere-crystals. Chemical tests are necessary to prove the identity 

 of the substance in these various forms. 



Not all substances, however, show this tendency to variation in 

 form of crystals, as, for example, caffeine, berberine, and still 

 other substances which show a tendency to uniformity in general 

 outhne. 



If, then, there is so much variation in the form and arrangement 

 of crystals of the same substance when artificially formed, to 

 what extent may not variation in form take place in bodies of 

 complex composition and therefore influenced by comj)lex attrac- 

 tions and repulsions ? Now while we see in the crystal a decided 

 tendency to uniformity of structure under similar conditions, yet, 

 admitting of modifications under varying conditions, we must 

 allow that in organized structures this tendency to uniformity is 

 modified over and over again. 



In the plant world similar variations are observed, not only in 

 forms of the elements (roots, stem, leaves, flowers, fruits and 

 seeds) comprising the individual, but also in cell-contents. In 

 some so-called species individuals vary greatly as regards form of 

 elements, as in oaks, violets, etc. In others a constancy is 

 observed, as in Enjthronium. In still others a variation in the 

 form assumed of some of the cell- contents is observed, as in the 

 crystals of calcium oxalate in Datura stranioniitm,^ while in other 

 crystals a constancy of form is observed, as with calcium oxalate 

 in the genus Viola. Even in the study of starch-grains one 

 observes a constancy in the form of the grains in all plants. 

 There is, however, a sufficient modification in some of the grains 

 in the reserve underground parts of such plants as potato, maranta, 

 etc., to justify one in pronouncing on the origin of the starch. 

 The same may be said of other substances, as calcium oxalate, 

 inulin and other carbohydrates, etc. 



^ The selection of certain constant forms of cell-contents or of cell- 

 walls would appear to be of as much, or greater, importance in 

 designating the limitations of a species as the outer form of ele- 

 ments, which it is evident are dependent upon the arrangement of 

 aggregates of substances making up the individual. As this 

 arrangement is due, on the one hand, to the chemical factors, food 



* The author, Proc. Amer. Assoc, for Add. of Science, 1899 ; see also 



Bulletin of Torrey Botanical Club, 1899. 



