THE AMERICAN BOTANIST 



15:5 



out into fairly recognizable groups, or shall the divisicjns be as 

 fine as they are in the violets where it is facetiously said that to 

 name a violet one must not only know when and w here it was 

 collected, but who collected it. 



Stereochemistry. — We are often at a loss to explain the 

 behavior of certain plants, but if the theories of those 

 scientists interested in stereochemistry are correct some 

 at least may be explained by the molecular structure of 

 their parts. Only three or four chemical elements are 

 found in the majority of plant substances. For instance, 

 such widely differing substances as starch and sugar, 

 vinegar and alcohol, wood and oil, mucilage and wax, are 

 composed of carbon, hydrogen and oxygen in varying 

 amounts. Still more remarkable, it is known that the 

 sugars, though made of exactly the same amounts of these 

 elements, are very different in their effects and in their 

 reactions with other substances. These differences are 

 now believed to be due, not to dilferent amounts of the 

 elements composing them, but to the different way in 

 which these elements may be arranged in the molecule. 

 Miescher has estimated that the serum globule molecule 

 may exist in a thousand million forms. Of the twelve 

 known forms of glucose, only dextro forms (that is, those 

 which rotate a beam of polarized light to the right) are 

 fermentable or capable of being used by certain low or- 

 ganisms for food. In other substances the dextro forms 

 may be untouched and other forms used, it thus appears 

 that the structure of the molecule is of immense im- 

 portance in the reaction of the organism or its parts and 

 this may explain why one substance is poisonous when 

 another exactly like it in composition is not, or why a 

 substance may poison one organism and not another 

 closely allied to it. By this theory mav be explained the 



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