HORMONES, VITAMINS, AUXIMONES 217 



from the conclusions of most investigators it would appear that 

 vitamins are as essential to plants as to animals; but the green 

 plant has the power to make its own vitamins in the same way 

 that it can make its own food. 



Since green plants can make their own vitamins, it is impossible 

 to grow them in a vitamin free medium, as can be done with 

 animals, and this makes the effects of vitamins upon plant growth 

 very much more difficult to study. But, from the results fairly 

 well established, it seems probable that saprophytes and parasites, 

 which do not make their own food, are like animals in that they 

 cannot make their own vitamins; they are dependent upon the 

 presence of these materials in the nutrient medium. Their food 

 must contain some vitamins of plant origin in addition to the 

 sugars, mineral salts, etc. This has been shown to be true for the 

 brown rot fungus of peaches and plums (Sclerotinia cinerea), for 

 yeast, and for many kinds of bacteria. The yeast, which itself is 

 an important source of vitamins, obtains them from the nutrient 

 medium upon which it grows, and it is probably for this reason 

 that barley malt is so stimulating to the growth of this fungus. 

 But this leads us back to the relation between vitamin B and bios, 

 where we have seen the difficulty in determining the relation be- 

 tween vitamins and similar substances and have noted some of the . 

 problems that arise in trying to determine what organic materials 

 a plant takes in from the surrounding medium and what ones it 

 manufactures within its own body. 



Auximones.— Bottomley (1917-1920) concluded that plants re- 

 quired something more than the elements generally admitted as 

 necessary for plant growth and found in ordinary culture solu- 

 tions. These growth promoters, of which the nature and composi- 

 tion were unknown, he called auximones. For his experiments he 

 used water plants such as Lemna and Azolla in order that the 

 ordinary difficulties involved in water cultures might be eliminated; 

 and he found that for good healthy growth, small amounts of 

 organic materials were necessary in the culture solution. The best 

 source of this organic matter is bacterized peat, which is peat pro- 

 duced from Sphagnum (a moss) that has been acted upon and de- 

 composed by nitrogen bacteria. This bacterized peat acts as a 

 food accessory rather than as a food, as shown by the very small 

 quantities required. For this reason it has been thought to be a 

 vitamin and has been so called by some workers. Rosenheim 



