Growth o/Lenma minor in Mineral Culture Solutions. 503 



From this diagram it is seen that plants which have been growing for some 

 time in either Detmer's solution or Detmer's solution plus auximones do not 

 respond immediately to the addition or removal of these substances to or 

 from the culture solution. There is about a week — a " reaction time " — 

 during which the previous tendency to decrease or increase is manifest before 

 the new factor becomes effective. 



An important point, which was noticed throughout the experiments, was 

 the fact that the greatest variation in the numbers and weights of the 

 plants in the various dishes each week appears in the control sets. Evidently, 

 where the plants are lacking auximones, there is a lack of uniformity between 

 the rate of multiplication and the increase in weight of the plants. In some 

 weeks growth-energy appears to be expended in multiplication, with little 

 corresponding increase in weight ; in other weeks increase in weight appears 

 to be attained at the expense of numbers. For example, in Table VI, 

 Series VI, Dish 58 in conductivity water shows a doubling of number from 

 the 10th to the 11th week, but the weight has only increased by about 

 25 per cent, during the same period. From the 11th to the 12th week the 

 same dish shows a further iucrease of rather more than 100 per cent, in the 

 number, but this time it is accompanied by an increase of more than 

 250 per cent, on the weight. Similarly, in Table II, Series II, Dish 4 

 in ordinary distilled water shows an increase in Dumber of practically 

 50 per cent, from the 4th to the 5th week, but the weight has scarcely 

 increased at all, while from the 5th to the 6th week, an increase in number 

 of about 60 per cent, is accompanied by an increase in weight of about 

 50 per cent. 



In the series containing auximones there is a much greater conformity 

 between the rate of multiplication and increase in weight. 



Conclusions. 



The foregoing experiments appear to justify the conclusions (1) that 

 bacterised peat contains certain organic substances which, when supplied 

 even in small quantities to Lemna plants growing in complete mineral 

 culture solutions, have a remarkable effect upon their growth ; (2) that in 

 these plants normal growth and multiplication cannot be sustained for any 

 length of time in the absence of these organic growth-promoting substances 

 or auximones : (3) that these substances are essential for the effective 

 utilisation and assimilation of the mineral nutrients supplied to these plants. 



It is highly probable that these auximones are organic decomposition 

 products, for bacterised peat is simply organic matter, already partially 

 decomposed by anaerobic action, which has been further decomposed by the 



