PROPI'RTIES OF WOOD 419 



which is combined with tannin in the manufacture of Russian leather ; 

 phlorizin in fruit trees; esculin in chestnut; coniferin in spruces; and 

 f raxin in ash. Tannins are found in barks ; organic acids, such as 

 gallic acid, in oak and chestnut; acetic acid; oxalic acid (especially 

 in the form of oxalates) ; carbides of hydrogen, such as essences or 

 resins (benzoin, sty rax). Among carbides of hydrogen should be 

 mentioned caoutchoucs. These are obtained from Ficus elastica of 

 the Indies, from Castilloa elastica of South America, Ficus Vogelii 

 of Senegal and Soudan, or from shrubs like Kickscia elastica of Guinea, 

 or vines like the Landolphia, Carpodinus and Calotropis of Senegal, 

 Guinea or Madagascar. 



Gutta percha is also found, as in the Palanquium gutta of the ]Malay 

 Peninsula and Borneo, and in the Mumusops balata, one of the Sapot- 

 aceae of the lower Orinoco. The best caoutchouc is the para of Brazil, 

 extracted from Hevea and Siphonia, of the family of Euphorbiaceae. 

 Latex, or vegetable milk, is an edible extract, such as the latex of the 

 Brosimum utile of America. 



Among the most widely distributed substances found in ligneous 

 vegetation is starch, which holds first place as a reserve food matter. 

 It is found in all the tissues of the trunk and roots, appears under as 

 many different forms as there are species, and in a single species it 

 differs according to its location in the pith or in the other tissues. The 

 quantity varies with the season. Starch appears in spring in the lig- 

 neous tissues (parenchyma), becomes more abundant in summer, and 

 reaches the maximum in the fall. It is reabsorbed at the end of 

 autumn, and appears again in March, being at the minimum in winter. 

 The nature of the soil affects the time of the appearance of starch. 

 Thus, in dry soils, it appears more rapidly and in larger quantities 

 than in wet soils. Mineral fertilizers affect the production of this im- 

 portant substance. Thus potassium compounds hasten the formation 

 of starch, and also tend to bring about rapid development of fruit. It 

 may even be said that they hasten the growth of fruit for the very 

 reason that they form starch rapidly. There is a remarkable correla- 

 tion between these two phenomena. Starch is more abundant in 

 branches bearing fruit than in other branches. Moreover, in cases 

 where starch is to be formed, potassium seems to be the favorite 

 stimulant. It gives the best results in the formation of tuberous roots, 

 especially potatoes. 



