CHAPTER XVII 

 HORMONES, VITAMINS, AUXIMONES 



Man shall not live by bread alone. 

 — Matthew 4:6. 



Within the past two decades, many experiments have been 

 made which show that in addition to the foods and allied materials 

 mentioned in the previous chapters, plants and animals need 

 still other materials in order to develop normally and completely. 

 These materials seem in some cases to be taken into the body 

 along with the food and in others to be manufactured inside the 

 body. Here, as elsewhere, plants are more independent and self- 

 supporting than animals. They are able to elaborate or make 

 most of these materials by the activity of their own protoplasm, 

 while animals are dependent upon plants for many (but not all) 

 of these substances. 



These materials not only have a helpful or beneficial effect 

 upon the physiological processes of the plant which produces them, 

 but also upon the animals which get these substances from the 

 plants. Depending upon their function, their method of opera- 

 tion, and the way in which they are produced, these accessory 

 factors have been variously treated by different workers under 

 the names of hormones, vitamins, and auximones. Whether 

 these are all distinct substances remains to be settled, but the 

 general nature of the materials will be briefly discussed. 



Hormones— Vochting (1878) noticed that if willow shoots are 

 cut and hung up in a moist place, roots will appear at the lower 

 end and shoots at the upper end.^ If some of the pieces are now 

 inverted so that the end formerly towards the root is uppermost, 

 roots will develop only at the upper end, where they are useless, 

 and stems only at the lower end. It thus appears that the one 

 end is a "root end" and the other a "stem end," and that roots 

 and stems develop at these places regardless of their utility or of 

 such external conditions as gravitation and light. Furthermore, 

 if a section of such a stem be broken up into pieces, each piece 

 will have a root and a stem end, the root end being the one nearest 



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