218 PLANT PHYSIOLOGY 



(1917), for example, found that the primrose, Primula malacoides, 

 when treated with an aqueous extract of only 0.18 g. of bacterized 

 peat, grew noticeably taller than plants not so treated. This 

 small quantity of peat contained only 0.02 g. of organic matter, 

 of which only about one-tenth or 0.002 g. was nitrogen, so it is 

 hard to understand to just what is due the stimulating action. 

 Likewise Ashby found that while Lemna lived indefinitely in a 

 purely inorganic solution, one part in five million of an organic 

 extract from horse dung was sufficient to significantly increase 

 the growth rate. He attributes this action to that of a catalyst. 

 Breazeale also found in manure " vitamin-like' ' substances, which 

 he thinks play the same role in plant nutrition that vitamins do 

 in that of animals. Auximones are, therefore, to be included in 

 the "nutrilites" of Williams. 



Since they stimulate the nitrifying and nitrogen-fixing bacteria in 

 the soil and at the same time depress the rate of denitrification, 

 it has been suggested that the auximones are important in the 

 synthesis of complex nitrogen compounds. At all events, bacter- 

 ized peat seems to contain some growth-promoting substances, 

 which are beneficial to various seed plants including the common 

 farm crops; but to what extent it can be used under field condi- 

 tions is one of the problems to be solved. How these auximones 

 operate is also still an open question, but it seems certain that 

 some plants do produce these auximones which are at least useful 

 to other plants if not absolutely necessary. 



It would not be surprising in the light of these investigations if 

 future researches showed that the auximones are either pro- 

 vitamins or else bear the same relation to plant nutrition that the 

 vitamins produced by plants bear to the nutrition of animals, as 

 suggested by Breazeale; and the similarity between the relation 

 of bios to yeast and that of auximones to Lemna is rather striking. 

 Like bios (and unlike vitamins) the auximones are not made 

 sufficiently rapidly by the higher plants to be of much use, but 

 must be obtained from the culture solution. 



These substances may be more necessary for green water plants 

 than for land plants because the former live normally in an en- 

 vironment where there is never any question of their lack. The 

 water plants have thus lost the power to manufacture their own 

 vitamins, while land plants not so favorably situated have had to 

 shift for themselves. But it should be added that Clark (1924- 



