Methods of Working 11 



Such water proved perfectly satisfactory so long as any necessary repairs 

 to the still were made with pure silver, but a toxic action set in directly 

 ordinary solder was employed. More recently a new tinned copper still 

 has been employed with good results, but this is somewhat dangerous 

 for general purposes, as in the event of the tin wearing off in any place, 

 copper poisoning sets in at once. The water is always filtered through 

 a good layer of charcoal as a final precaution against impurity. 



In the Rothamsted experiments no attempt is made to carry on the 

 cultures under sterile conditions. Bottles of 600 c.c. capacity are used, 

 after being thoroughly cleaned by prolonged boiling (about four hours) 

 followed by washing and rinsing. The bottles are filled with nutritive 

 solution and the appropriate dose of poison, carefully labelled and 

 covered with thick brown paper coats to exclude the light from the 

 roots and to prevent the growth of unicellular green algae. The corks 

 to fit the bottles are either used brand new or, if old, are sterilised in 

 the autoclave to avoid any germ contamination from previous experi- 

 ments. Lack of care in this respect leads to diseased conditions due to 

 the growth of fungi and harmful bacteria. Two holes are bored in each 

 cork, one to admit air, the other to hold the plant, and the cork is cut 

 into two pieces through the latter hole. 



The seeds of the experimental plants are " graded," weighed so that 

 they only vary within certain limits, e.g. barley may be '05 '06 gm., 

 peas '3 '35 gm., buckwheat '02 '03 gm. In this way a more uniform 

 crop is obtained. Great care is needed in selecting the seeds, the 

 purest strain possible being obtained in each case. With barley it has 

 always proved possible to get a pure pedigree strain, originally raised 

 from a single ear. In this way much of the difficulty due to the great 

 individuality of the plants is overcome, though that is a factor that 

 must always be recognised and reckoned with. The seeds are sown in 

 damp sawdust clean deal sawdust, sifted and mixed up with water 

 into a nice crumbly mass and as soon as they have germinated and 

 the plantlets are big enough to handle they are put into the culture 

 solutions. Barley plants are inserted in the corks with the aid of a little 

 cotton wool (non-absorbent) to support them, care being taken to keep 

 the seed above the level of the water, though it is below the cork. With 

 peas it is impossible to get a satisfactory crop if the seed is below the 

 cork, as the plant is very prone to bacterial and fungal infection in its 

 early stages, and damp cotyledons are fatal for this reason. Conse- 

 quently the mouths of the bottles are covered with stout cartridge paper, 

 the pea root being inserted through a hole in the paper, so that the 



