36 



orcinol good root development is ultimately able to take place, and 

 there is a corresponding improvement in the shoot growth. Barley is 

 more sensitive than peas, as recovery seldom takes place, and even with 

 resorcinol and orcinol the roots make very little improvement. 



The lower strength M/ioo X 1 2 also shows clearly the difference 

 in the action of the phenols, the range of variation being considerable. 

 In nearly every case an initial check is produced, but the degree of 

 injury varies very much. Resorcinol at this strength has very little 

 effect on peas as growth is fairly good from the beginning, and with 

 orcinol also strong growth is made. Phenols cause the roots to become 

 bunchy through the development of short laterals, but recovery from 

 the toxic effects is so complete that the plants make nearly as much 

 dry weight as the controls. Recovery from the effects of most of the 

 other substances is variable in amount, but pyrocatechol is so poisonous 

 that very little growth is made up to the end. Barley behaves in much 

 the same way as peas, though owing to its sensitiveness the recovery 

 is not always so complete as in the case of peas. 



Lower concentrations of all the poisons seem to exercise no 

 injurious action on growth. 



The root recovery observed in strong solutions suggests that in 

 these cases the poison acts largely by suspending the activities of the 

 plant, paralysing it without killing it outright. Consequently, when 

 the paralysing effect wears off or the concentration of the solution is 

 somewhat reduced by oxidation the plant reasserts its vitality, struggles 

 to put out lateral roots, and frequently succeeds so well that fairly 

 good growth is eventually made. 



No signs of stimulation have been observed in the case of any of the 

 phenols tested, except that barley plants in the dilute solutions cf 

 orcinol looked better than the controls before they were cut. This 

 appearance was not corroborated by the dry weights. 



When the plants were killed or badly injured by high concentrations 

 of the phenols, moulds appeared very rapidly on the dead roots and in 

 the solutions, except only in the strongest solutions of phenol and the 

 three cresols. With the latter no mould formation set in during the 

 whole course of the experiment, but with phenol the antiseptic action 

 ceased after some time and moulds eventually appeared. Where no 

 root injury was caused no moulds grew in any case. 



XXVIII. " Effect of the Concentration of the Nutrient Solution on 

 the growth of Barley and Wheat in Water Cultures.''^ 

 Winifred E. Brenchley. Annals of Botany, 1916. 

 30, 77-90. 



For some years past much discussion has taken place as to whether 

 the concentration of the nutrient solution has any appreciable effect 

 upon plant growth, and at the present time the controversy is far from 

 settled. 



A number of water culture experiments have been made to see if 

 further information could be obtained on the effect of varying con- 

 centrations of nutrient solutions upon growth, barley being used as the 

 test plant in three series of experiments, and wheat being grown in a 

 fourth. 



Four strengths of solution were used ; N, ordinary strength (called 

 N.) containing 3 grms. of nutrient salts dissolved in one litre of 



