I'KOPKIITIKS OF WOO]). 



Sugar contained in the sap of certain species of maple, birch 



and palms is of economic value. In maples the conversion 

 of starch into dextrin and sugar occurs only in winter with 

 temperatures below freezing-point and so rapidly, that from 

 January onwards, on days when it does not freeze, sap con- 

 taining sugar exudes from wounds in the trees. The yield of 

 sugar appears to depend on turgescence and pressure ; sap 

 does not exude by gravitation but is pressed out of the sap- 

 wood. As soon as frost returns the sap ceases to exude ; 

 all maples yield fairly considerable quantities of sweet sap, 

 which can be tapped without any apparent injury to the tree 

 or the wood. When the buds open the annual exudation 

 of sap ceases. Even European maples yield an agreeably 

 scented syrup ; if this were boiled, sugar could be made easily. 

 This industry is largely developed in North America, and is 

 referred to under the heading of the utilization of minor 

 produce. The sap of maples contains iive per cent, of sugar 

 and more, that of birch, hornbeam and lime-trees, hardly two 

 per cent. Fermented birch- sap is a drink. 



Grains of sugar appearing on fresh wounds of the sugar- 

 pine (Pintis Lawbcrtiana) are used in medicine. 



Starch is stored in the parenchymatous cells of living trees ; 

 in their external woody zones it is dissolved annually and 

 used for new growth ; according to Hartig, in old living wood 

 (containing plasma) it accumulates until there is a seed-year, 

 so that the periodicity of seed-years coincides with the maxima 

 accumulations of starch. This statement is admissible only if 

 it can he proved that in specially favourable warm years (lS',)i>, 

 1898, 1894), several successive seed-years can result from the 

 accumulation of starch in the inner living zones of the same 

 tree. Mayr believes that bright warm summers produce so 

 much starch and other formative material as to suilice for the 

 production of flower-buds, without drawing upon the resources 

 of preceding years. 



Starch increases the nutritive power of wood and together 

 with mineral salts and albumen is stored chiefly in the liner 

 branches and twigs, so that these tree-par! s are specially 

 nutritive for cattle and game. The older tree-parts are poor 

 in nutriment, but in years of scarcily they may be mixed with 



