250 WATER-CULTURE. 



satisfactory results ; in man}- cases plants have been carried 

 safely throughout their whole development from seed to seed. 

 The principal difficulties arise from the invasion of moulds, and 

 from the continual changes which the nutrient solution under- 

 goes. 



670. In Tharandt, 1 where the method has been very success- 

 fully applied in numerous series of cultures, the following out- 

 fit suffices: (1) small glass vessels covered with gauze, upon 

 which the seeds swollen by twelve hours' immersion in water, 

 and subsequent!}- sprouted on filtering-paper, are placed for 

 further development ; (2) wide-mouthed vessels of the capacit}', 

 respectively, of one, two, and three liters, each of which is pro- 

 vided with the spring and cork already described. 



671. By the careful use of these simple appliances the role 

 which each of the ash constituents plays in the life and growth 

 of plants has been ascertained. But although there is a sub- 

 stantial agreement among experimenters as to the more impor- 

 tant points, there are a few unsettled questions. 2 



672. Normal nutrient solution. It is plain that an aqueous 

 solution of the salts necessary for the most active and complete 

 development of the plant should have these salts in the right 

 proportion. The solution advised for ordinary use in the above 

 experiments is generally known as the Tharandt normal-culture 

 solution. Nobbe 8 gives the proportions as follows : 



1 Success hi water-culture demands the closest attention to all the external 

 conditions of the plant. The amount of light and heat must be carefully regu- 

 lated, and the plants must be kept free from any insects and parasitic fungi. 

 The latter is one of the most difficult and discouraging tasks connected with 

 the method of experimenting. In order to secure the best surroundings for 

 the cultivation of plants in water, a heavy table moving with wheels on rails 

 has been employed at the experiment-station at Tharandt ; upon this the glass 

 vessels can be carried with the least liability to jarring, from the open air in 

 the daytime to a suitable protection at night or duiing wet weather. 



2 Moreover it is to be borne in mind that the conditions of water-culture 

 are very unlike those of ordinary culture in respect to the surroundings of the 

 roots themselves, and it is believed that to this difference of conditions may be 

 ascribed some of the unsettled questions. The root-hairs developed in contact 

 with moist particles of soil are not the same as those grown in water alone. 

 To avoid this possible source of error, various finely divided substances have 

 been suggested as a proper support for the roots and rootlets ; for instance, 

 the charcoal from sugar, powdered quartz, etc. When these are employed, the 

 roots of the plant are made to grow directly in the artificial soil which is 

 watered with the experimental solutions. 



3 By the use of this solution buckwheat plants can be carried through their 

 entire development, as is shown by Nobbe, in Versuchs-Stationen, 1868, p. 4. 

 He arranged nine plants in five vessels, each of three litres capacity, in such 



