THE MOLECULAR FORCES IN PLANTS. 239 



different kinds of maize do not behave in the same manner in this 

 respect. Perhaps also it is not a matter of indifference whether 

 the roots develop in spring water, or in distilled water, or whether 

 they are grown in darkness or light. I found that the main roots 

 of peas grown in distilled water, in absence of light, were devoid 

 of root-hairs, while roots grown in garden soil were very well 

 supplied with them. 



1 See Sachs, Handbuch der Experimentalphysiologie der Pflanzen, 1865, p. 

 185. 



2 See Fr. Schwarz in Untersuchungen aus d. botan. Institut zu Tubingen, Bd. 

 1, H. 2. 



89. The Absorption of Mineral Substances from Nutrient 

 Solutions by Roots. 



In my Lehrbuch der Pflanzenpliysiologie, p. 136, I have already 

 pointed out that the conditions relating to the absorption of 

 mineral substances by roots from solutions of food stuffs are of a 

 very complicated nature, and are still by no means satisfactorily 

 elucidated. The result which is finally attained is not only de- 

 pendent on the concentration of the solution, the nature of the 

 food stuffs employed, their consumption in the plant, etc., but 

 also on the nature of the plant, the external conditions under 

 which it is growing, and many other circumstances. Further 

 investigations, with careful analysis of the whole phenomenon, 

 will be required in order to gain fuller information. In this place 

 we will consider the absorption of mineral substance by roots 

 which have at their disposal an aqueous solution of a single salt, 

 a question which is certainly of interest in connection with the 

 absorption of mineral substances from complete food solutions. 



We soak a number of well-developed seeds of Phaseolus or Zea, 

 germinate them in moist sawdust, and determine the weight of 

 each seedling. Glass vessels of rather more than 100 c.c. capacity 

 are fitted with perforated corks, and in the holes of these we fix 

 the seedlings singly by means of cotton wool. Some of the vessels 

 have been previously supplied with 100 c.c. of a 0'250 per cent, 

 solution of Potassium nitrate, others with a 100 c.c. of a 0'050 per 

 cent, or 0'025 per cent, solution of that salt. We now weigh 

 the vessels with their seedlings, and then leave them in a well- 

 lighted place until they have lost about 50 gr. in weight, so that 

 about half of the fluid originally present has been sucked up by 



