THE AMERICAN BOTANIST 7 1 



sugars, starches, acids, fats, glycerins and various others — 

 have molecules with the atoms in chains, while those which 

 may he regarded as waste products or products concerned with 

 the metabolism of the plant — such as turpentines, camphors, 

 pigments, resins, rubbers, tannins, glucosides, and alkaloids — 

 have molecules of the cyclic type. It is assumed that this latter 

 group of substances has been derived from the first group by 

 the changing of their molecules from open chains to rings by 

 the plants. Furthermore, the substances in the first group can 

 pass freely into the cells, but those with cyclic molecules find 

 it difficult or impossible to do so. This conception of the form 

 of the molecule may help to an understanding of the differ- 

 ences between starch and cellulose. These two substances 

 have the same chemical formula and yet it is usually easy to 

 distinguish between sawdust and breakfast food, however 

 much the former is camouflaged. The essential difference, 

 according to Pictet, is that the molecules of starch are in chains 

 while those of cellulose are cyclic. The constituents of coal 

 tar all have cyclic molecules and it is from such substances 

 that an immense number of dyes, drugs, and other useful 

 substances are manufactured. Protoplasm, itself, is supposed 

 to begin with molecules in chains and to end by stabilization 

 with its molecules of the cyclic type. 



