TRANSACTIONS OF SECTION K. 725 



curve does not represent comparable rates at different temperatures, since he 

 made liis measurements not at specified stages of plasmolysis but after a fixed 

 time interval (two hours), when the pieces at low temperatures were at an early 

 stage, while those at high temperatures were completely plasmolysed. 



4. The Respiration of Partly-dried Plant Organs. By A. Malins Smith. 



Plant-organs, such as the leaves of the Snowdrop, stem-tips of Tropccolum, 

 and young stems of Asparagus, were deprived of varying proportions of the 

 water they contained by drying in a vacuum desiccator at a pressure of about 

 half an atmosphere. In the partly dried condition their CO2 output was 

 measured by passing over them a stream of CO2 free air and analysing the out- 

 going air by means of baryta in Pettenkofer tubes. Confirmatory experiments 

 were made with plants dried at ordinary atmosphere pressure. The results 

 were as follows : — 



(1) When deprived of from ^ to ^ of the total water contained, the respiration 

 of the dried plants was increased over that of normal plants. 



This occurred in the case of stems of Tropaolum, stems and roots of Bean 

 seedlings, and in the leaves of the Snowdrop. A very slight increase was found 

 in stems of Sempervivum, 



No increase was found in young stems of Pseony or in young stems of 

 Asparagus. 



On account of the time taken in drying, the first phase of normal respiration 

 was completed before the plants were tested, and all the results apply to the 

 second phase, called by Dr. F. F. Blackman the ' protoplasmic ' respiration, 

 when the reserve food supply of the organs has practically disappeared. 



(2) Experiments to find whether this increased effect was a reversible one 

 have not yet been conclusive, but so far there is no evidence for reversibility. 



(3) A thorough investigation of the course of respiration with varying 

 amounts of water lost, a fresh lot of plants being used for each test, showea 

 that the resulting respiration could be divided into three phases : — 



(i) On removing small percentages of water, from to about 30 per cent. 



of the water originally present, the respiration gradually increased in 



proportion to the amount of water removed, 

 (ii) In the second phase the respiration remained steady at the increased 



level. The length of this phase varied, lasting from 25 or 30 per cent. 



to 50 or 60 per cent, loss of water, 

 (iii) From 50 to 60 per cent, loss up to complete dryness the respiration 



decreased again proportionally to the amount of water lost. The curve 



of results indicated that in all material the plants continued to give out 



some CO2 as long as any water was left in the tissues. 



There were minor differences between the results in the two principal cases 

 investigated, namely Snowdrop leaves and Tropccolum stems, but in each case 

 the three phases were clearly marked. 



The meaning of the increased ' protoplasmic ' respiration in partly dried 

 material is obscure. Harden and Paine have shown that the activity of 

 glycogenase in the autofermentation of yeast is increased by simple drying. 

 Possibly the increased respiration shown in these experiments may be due to 

 the increased activity of one or more enzymes. Further experiment on that part 

 of the curve of CO2 output relating to plant organs which are almost perfectly 

 dry may throw some light on the question of residual vitality, and may perhaps 

 have interesting connections with the condition of air-dry seeds. 



Demonstrations were given in the Botanical Laboratories of the University 

 by Dr. Sarah M. Baker, Professor W. B. Bottomley, Professor F. O. Bower, 

 Professor D. Ellis, Professor Julius MacLeod, Professor F. W. Oliver, 

 Professor T. G. B. Osborn, Mrs. Edith M. Osborn, and Dr. Marie C. Stopes in 

 connection with their papers : also by Miss N. Bancroft {Petiole of Zygopteris 



