494 SECTIONAL TRANSACTIONS.— K. 



copper, cobalt and nickel the sulphates and chlorides have shown relatively- 

 slight differences in action, though these were sometimes significant with 

 regard to the concentration at which marked toxicity occurred. 



Individual species respond according to the poison used. With barley, 

 copper was more poisonous than either nickel or cobalt, but the differences 

 were relatively small. With broad beans, however, cobalt was much more 

 toxic than nickel or copper, particularly as sulphate. Earlier experiments 

 had shown that peas were more sensitive than barley to copper and arsenic, 

 whereas barley was less able to withstand zinc, boron and manganese. The 

 morphological response to poisoning depends on the element concerned, 

 root and shoot growth being variously affected. Individuality of plant 

 response is frequently shown by great variation in growth in borderline 

 concentrations just below those causing marked depression of growth. 



Afternoon. 

 Joint Discussion on The mechanism of evolution {continued) (2.15). See 

 under Section D. 



(concurrently with above.) 



Dr. J. Barker. — Temperature and the starch! sugar balance in potatoes (2.15). 



Since the researches of MuUer-Thurgau (1882 and 1885) it has been 

 generally recognised that sugar accumulates in potatoes which are stored at 

 low temperatures and that the accvimulated sugar disappears when the potatoes 

 are returned to higher temperatures. These changes in the sugar content 

 were attributed by Muller-Thurgau to differences in the temperature- 

 coefficients of the three reactions ; (a) hydrolysis of starch to sugar, (b) con- 

 densation of sugar to starch, (c) consumption of sugar in respiration. Recent 

 experiments suggest, however, that the influence of temperature on the 

 balance between these three reactions cannot be interpreted as due solely to 

 differences in their temperature-coefficients. 



Evidence has been obtained showing that the accumulation of sugar at low 

 temperatures is associated with a change in the metabolic state which persists 

 for a short time when the temperature is increased again ; this change is 

 provisionally conceived as an activation of the hydrolytic system. 



The changes in sugar content are shown to be dependent not only on the 

 actual temperature of storage (a characteristic already well recognised) but 

 to be markedly influenced by the previous temperature-history. 



Mr. R. S. DE Ropp and Prof. F. G. Gregory. — The hormone system of 

 the rye grain (2.45). 



The embryo of the rye grain receives from the endosperm, during the 

 first few hours of soaking, hormones which influence growth of roots and 

 coleoptile and the rate of response of these organs to gravity and light. A 

 factor influencing the response of the embryo to added hetero-auxin has 

 been noted. 



The aleurone layer of the grain appears to be the source from which the 

 scutellum receives the stimulus for diastase production. 



The aleurone and endosperm form with the embryo a complex inter- 

 acting system. Removal of the aleurone layer after the grain has been 

 soaked for an hour causes growth of the embryo to be inhibited. Subse- 

 quent growth of such embryos is abnormal. 



A similar effect is produced by removing the endosperm from grain 

 soaked for one hour leaving the aleurone in contact with the embryo. 



