386 SECTIONAL TRANSACTIONS.— K. 



Dr. WiNiFRteD E. Brenchley. — The Influence of Traces of Various Elements 

 ujpon Plant Growth. 



The importance of traces of the rarer elements found in plants is graduallj' 

 becoming apparent, as it is demonstrated that in certain cases they have a definite 

 physiological function in relation to metabolism. Many elements are known to 

 improve growth if presented in sufficiently small amounts, but it is now evident that 

 minute traces of boron, manganese, zinc, &c., are as essential to the development of 

 some plants as the major nutrients, phosphorus, potash and nitrogen. There is 

 some evidence to indicate that the discrepant results obtained by various investi- 

 gators may be due, partly at least, to environmental conditions such as variations 

 in light intensity. Strong insolation often tends to increase the harmful effect of 

 deficiency of certain elements, as is shown by the different degree of development of 

 broad bean in water culture in dull spring and bright summer weather in the absence of 

 boron, and by the chlorosis induced in peas when the iron is rendered less available for 

 chlorophyll development by too bright sunlight at critical periods. Small doses of 

 copper sulphate have been successfully used to raise crops on infertile peat in Florida, 

 but English peats, both acid and alkaline, have so far failed to give a similar response 

 with the same crop plants. 



The exact physiological function of these essential traces of elements has not yet 

 been fully determined. Manganese is assumed to be concerned with enzyme activity 

 as it is a constituent of laccase, boron is associated with the development of meriste- 

 matic tissues, and appears to be bound up with the calcium nutrition of the plant, 

 and copper in some cases may be comparable to iron in plant economy. Claims have 

 been made for the essential nature of traces of a considerable range of elements 

 including iodine, fluorine, aluminium and zinc, but more investigation is needed to 

 determine whether these are merely stimulating agents, or whether they play a 

 definite part in the metabolism of certain plants, as has been shown with boron and 

 manganese. 



Afternoon. 



Excursion to the National Botanic Garden, Kirstenbosch. 



Thursday, July 25. 

 Joint Discussion with Sections D and I {q.v.) on The Nature of Life. 



Miss A. V. DuTHiE. — The Life-history and Morphology of Riccia purpu- 

 rascens. 



Mrs. M. R. Levyns. — The Problem of the Rhenoster Bush. 



Dr. Elizabeth S. Semmens. — Hydrolysis of Starch in the Living Plant. 



Starch in the mesophyU of a young and healthy leaf is shown to undergo hydrolysis 

 after four or five hours' exposure to light polarised by a Nicol's prism or by reflection. 

 On a leaf so exposed, after staining with iodine, a light patch is seen, corresponding 

 in shape and position with the aperture of the Nicol. 



Not only is starch so affected, but other highly organised substances, such as 

 glucosides, can be broken down. 



A deep crimson leaf of Beta vulgaris, exposed as above for six hours, after dipping 1 

 in weak sulphuric acid, was soaked in amyl alcohol. Red drops of colouring matter I 

 dissolved out at the exposed area and a lighter patch was seen, showing that the! 

 anthocyanin had hydrolysed to anthocj^anidin and had been dissolved by the amyl 

 alcohol. 



As the vertical light of the evening and morning sky is strongly polarised, this fact] 

 has an important bearing on plant metabolism. 



To demonstrate this effect, patches of small leaves, such as ' Lucerne,' were exposed ] 

 to the afternoon sky light from 4 to 6 p.m., but shielded from the setting sun. Thesej 



