THE WORK OF STEMS 259 



of the starch has been converted into sugar; in the 

 spring, with the approach of warmer weather, the 

 starch reappears and remains until it is used up by 

 the growth of the new leaves and branches. On 

 account of the starch which they contain in winter, 

 such trees as the Oak, Willow, Hazel, Lilac, etc., are 

 called starch trees. On the other hand, many trees, 

 such as the Linden, Birch, etc., contain no starch in 

 midwinter; it has been transformed into fat, as is 

 indicated on placing sections in alcanna tincture. ^ 

 Such trees are called fat trees ; on the approach of 

 warmer w^eather in spring the fat is changed back into 

 starch. Does the temperature seem to control these 

 changes? Bring in a branch of Linden in midwinter 

 and test for starch ; set it in a jar of w-ater in a warm 

 room, and after three or four weeks test again. 



When the buds are preparing to unfold in the 

 spring, the sap begins to run. We can observe this 

 especially well in the Sugar Maple, Birch, etc., and 

 here the taste of the sap shows that it contains a 

 considerable quantity of sugar. In this case, then, 

 the sugar travels upw^ard in the w^ood ; this sugar, as 

 we can easily convince ourselves, comes from the 

 transformation of the starch and serves to supply the 

 young leaves and branches with material for their 

 vigorous spring growth. Investigate other trees, test- 



1 This is obtainable at dm^-stores. It is made by placinjir alcanna root in 

 alcohol \intil the coloring matter is extracted. It has the property of staining 

 fats and oils red. 



