SECTIONAL TRANSACTIONS.— K. 389 



Necrosis was found in stem, petiole and the main veins of the leaf-blade, but not in 

 the finer vein endings. It may consist merely of a swelling of the middle lamella, 

 which eventually more or less obliterates the lumen, or may be followed by the 

 deposition of ligno-celluloses. In many cases the radial walls of the phloem are much 

 elongated. 



Phloem necrosis, except in the most extreme cases of leaf-roll, does not occur to 

 a sufficient extent to account for the excess accumulation of starch in the leaves, nor 

 for the external symptoms of the disease ; it is, however, possible that necrosis marks 

 the end point of phloem disease and not its inception. Necrosis was not observed in 

 plants affected with ' blackleg ' or mechanical ' wilt.' 



Starch accumulation in leaf -roll leaves is a reliable method of diagnosis in cases 

 where the external symptoms of leaf-roll are somewhat doubtful, providing that 

 whole leaves are used and that other diseases, which also induce excess accumulation 

 of starch, are known to be absent. 



Excess starch accumulation begins prior to rolling of the leaves, but pathological 

 changes of the phlcem may occur concurrently. By excluding light for six days, 

 leaf-roll plants have been partially depleted of starch, but in a manner quite different 

 from depletion in healthy plants. 



A rough comparison of sugar and starch contents of healthy and leaf-roll leaves 

 has been made at bi-hourly intervals during the night. At midday healthy leaves, 

 which were full of starch, contained little or no reducing sugars. Conversion into 

 such sugars began in the late afternoon, and by 5 a.m. the whole of the starch had 

 been depleted. On the other hand, the leaf-roll leaves contained not only more 

 starch at midday than the healthy ones, but also very much more reducing sugar. 

 Translocation was very slow in diseased plants during the night, and the reserve starch 

 was apparently not drawn upon at all. 



Miss Margaret Martin. — The Influence of Ultra-Violet Light on the 

 Structure of Plants. 



Observations have been made on the growth and structure of plants irradiated 

 with a Hewittic ' Ulviarc ' quartz mercury vapour lamp for short periods daily, as 

 described by Miss Westbrook in a previous communication. 



Plants of Arachis and Voandzeia showed definitely harmful effects when irradiated 

 with the unscreened lamp for daily periods of 10, 5, 2 minutes and 1 minute respec- 

 tively at a distance of three feet, over a period of five weeks. Some of these effects 

 are described, and the reaction to such doses is followed at different stages in these and 

 other plants. 



When the daily period of irradiation was reduced to 30 seconds at a distance of 

 5 or 8 feet, there were indications of a stimulating effect upon plants of Trifolium and 

 Pelargonium. 



Voandzeia, Pelargonium and other plants have also been irradiated with the sama 

 light filtered through various screens, and the effects of isolated regions of the spectrum 

 have been investigated in this way. The results are discussed in connection with 

 the difficulties of obtaining screened light of comparable intensity. 



Mi&s Alison Westbrook. — The Influence of Ultra-Violet Radiation on the 

 Growth of Plants. 



Recent physiological research and medical experience have shown repeatedly the 

 value of artificial ultra-violet light in remedial treatment and in maintenance of health. 

 Much less is known of its action on plants, but stunting and other harmful effects have 

 been reported. 



Observations have now been made on the growth of plants as influenced by 

 irradiation varying from \ minute to 15 minutes daily with a Hewittic ' Ulviarc ' 

 quartz mercury vapour lamp, the spectrum of which shows lines in the ultra-violet 

 from fi.ji.226-400, together with intense bands in the violet, blue, green and yellow. 

 Distances were chosen such as to avoid local heating at the surface of the plant. In 

 other experiments various screens have also been employed, transmitting only certain 

 parts of the spectrum : — 



1. Clear Vitaglass : transmitting 90 per cent, of the visible rays and a proportion 



of ultra-violet rays of 20-30 per cent, in the region of (j.[j.290. 



2. Blue Uviol : transmitting the blue-violet and ultra-violet rays to about [X|J.290 



