May, 1914.] Starch Reserve in Birch and Maple. 319 



small tree on the south bank of "Mirror Lake," while producing 

 a sap of lowest concentration, yielded more sugar per hour than 

 any other of the inaples. Under the varied conditions of the 

 experiment, all maples produced a clear creamy white sugar 

 in which little difference in taste was noticed, although the silver 

 maple. No. 4, was in flower at the time. The average concentra- 

 tion of sugar in the sap for the maples was 2.2 %. These results, 

 together with those of Professor Jones, make it probable that the 

 Bonn Text Book is in error in rating the average % for the North 

 American maple at yi of 1%. The average yield of maple sugar 

 per hour was 4 grams. 



At the close of the sap rvm, April 10, there was almost no corro- 

 sion of the starch granules in any of the woody tissues of the sugar 

 maple. There was little starch in any of the tissues of the bark 

 of the young twigs ; but starch was still abundant in the same tis- 

 sues of the root. On April 24, the flowers ha,d fairly opened, and 

 were so numerous as to give the crown of the tree a general green 

 color. Starch had been used from the branches examined, which 

 showed less than 9 annual rings of wood. 



In summary, it may be stated that, previous to bud growth, 

 little starch had been used, the most pronounced changes being 

 confined to the bark of the stem. While buds were swelling, the 

 starch was used from twigs showing less than 3 annual rings of 

 wood. By the time flowers were fully formed, starch had been 

 used from all portions of the stem showing less than annual rings 

 of wood. In other words, starch has been used first from the 1- 

 year old twigs; then, from those portions of the branch showing 

 two annual rings of wood; then, from portions showing 3 annual 

 rings, and so on progressively down to that portion of the branch 

 showing 10 years of wood. Beyond this, as in the root, no mark- 

 ed changes have occurred as yet. 



I am indebeted to Mr. H. Udovitch, who has generously aided 

 in collecting data in the flow of sap, and who has supplied the in- 

 formation concerning the use made of the birch in Russia. 



EXPLANATION OF PLATE XV. 



Figure 1. Cross-section of 1-year old twig. 

 Figure 2. Cross-section of root. 



11. m. uniseriate medullary raj'. 



h. m. biseriate medtillary ray. 



/. trachea. 



d. p. differentiated pith zone. 



p. undifferentiated pith cell. 



w. /. wood fibre. 



■w. p. wood partnchyma. 



h. p. bordered pit in section. 



5. p. simple pit in section. 



