ROBBINS: VITAMINS 117 



min Bi) was isolated by Jansen and Donath in 1926 and became generally 

 available in 1934. In that year Schopfer showed that the bread mold Phy- 

 comyces would not grow unless it was furnished with minute traces of this 

 vitamin. With this convincing demonstration as a basis and the isolation of 

 additional vitamins in chemically pure form our knowledge advanced rapidly. 



Now we realize that plants are not so philanthropic as they once seemed. 

 We know they too need vitamins, but more provident than animals, most 

 plants make their own vitamins. Only the minority, and these chiefly the lower 

 plants, suffer from vitamin deficiencies; that is, they cannot develop unless 

 the material upon which they grow contains some of the necessary vitamins 

 which, of course, must come from some other kind of plant or from an animal 

 which has obtained them from a plant. Some bacteria, yeasts and molds need 

 to be supplied with vitamins. Few, if any, of the trees, vegetables, flowers and 

 other green plants benefit from having vitamins supplied them. To the best of 

 our knowledge they make all they need. 



You may ask whether this means, in spite of the considerable publicity on 

 this subject, that supplying green plants with vitamin Bi or other vitamins is 

 not beneficial ? I would answer this question in this way. The application of 

 vitamins to trees, flowers, vegetables and other green plants is still in an ex- 

 perimental stage. Some investigators have reported beneficial results on some 

 kinds of plants and not on others. Many have obtained negative results. We 

 must conclude either that the conditions under which vitamins are beneficial 

 to green plants are poorly understood or that their application does not bring 

 favorable results. Certainly the use of vitamins in horticultural practice does 

 not accomplish the miracles some would have us believe, and no reputable 

 horticulturist on the basis of the evidence now at hand would recommend their 

 use under normal garden and greenhouse practice. 



In discussing the relation of vitamins to plans there are a good many 

 questions we might ask. For example, what is a vitamin, how were they dis- 

 covered, how do we know plants need vitamins and how many vitamins do 

 plants need, what plants must be supplied vitamins and what do the vitamins 

 do in the plant, how much of a vitamin is needed and is there a substitute for 

 a particular vitamin — something just as good? I can't answer all these ques- 

 tions for any one vitamin, but some of them can be answered by discussing a 

 particular vitamin, and I have selected three, thiamine or vitamin Bi, py- 

 ridoxine or vitamin Bq and biotin or vitamin H. 



Thiamine. Thiamine or vitamin Bi is a white crystalline substance con- 

 taining carbon, hydrogen, nitrogen, oxygen and sulfur. Its empirical formula 

 is C12H16ON4S. Its structure is known and between 25 and 30 tons are now 

 made annually in chemical laboratories in this country. In 1935 thiamine cost 

 $300 per gram which is at the rate of $135,000 per pound. With the discovery 



