- RECENT ADVANCES IN SCIENCE 205 



this work with the observations of Craib appears desirable, 

 although, in view of the relatively small seasonal changes of 

 water content of sap wood, and the high permeability of the 

 wood to water, it may be doubted whether there is anything 

 of the nature of competition for water by the tissues. 



Some experiments with reference to the winter storage of 

 starch and fat have been carried out upon herbaceous plants 

 growing under the severe conditions of Western Canada. 

 Gwynethe M. Tuttle {Annals of Botany, 191 9, 33, 201-10) has 

 found it possible to influence the starch fat ratio in evergreens. 

 Normally, starch disappears in autumn and oil takes its place as 

 a food reserve, starch reappearing with the advent of the grow- 

 ing season. It was found that these changes could be induced 

 at will in the case of Linncea by exposure to suitable tempera- 

 ture conditions. Starch reappeared in oil-containing cells 

 within two days of their removal from the outside cold to the 

 laboratory temperature of 20° C. Reappearance of oil and 

 loss of starch can then be induced by exposure to moderately 

 low temperatures (about freezing-point), but subjecting the 

 plants at once to the winter temperature of 15° to 30° C. below 

 zero results in death. This work emphasises the point pre- 

 viously noted — namely, the protection against freezing derived 

 by the plant from this capacity to vary the nature of its food 

 reserves. The question of the formation of starch from oil, 

 and vice versa, is also discussed in this paper, and on the basis 

 of the localisation of starch at its first appearance (as if sur- 

 rounding an oil globule), and of the occurrence of lipase and 

 oxidase in the leaf, the author inclines to the view that direct 

 transformation takes place. The records of this investigation 

 are continued by F. J. Lewis and Gwynethe M. Tuttle {Annals 

 of Botany, 1920, 34, 405-16), who carried out serial determina- 

 tions of osmotic pressure, electrical conductivity, and amounts 

 of sucrose, maltose, and glucose in leaf tissues of both woody 

 and herbaceous evergreens. They hesitate to record any 

 correlation between these values and the temperature records 

 on the results of the work of one season only, but they note 

 the occurrences of maximum osmotic concentration either in 

 December or in March. They found, as Chandler did, that 

 the osmotic pressure was due chiefly to non-electrolytes, the 

 concentration of electrolytes changing but little throughout 

 the season. Sugars disappear progressively from winter to 

 summer, glucose being the last to be removed. An important 

 fact in relation to resistance to frost-injury is revealed by 

 supercooling experiments. Whereas the sap extracted from 

 leaves of Pyrola froze at about -3° C, the leaves themselves 

 could be cooled to -32° C. before freezing. A significant 

 observation is also recorded regarding the chloroplast, which 



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