SEASONAL VARIATION IN THE FOOD RESERVES OF 



TREES* 



By John F. Preston and Frank J. Phillips. 



INTRODUCTION. 



One of the earliest records of the reduction of starch in the 

 cortex and phloem of the stems of woody plants in winter is con- 

 tained in a report by Mer^ in 1879. This author examined but 

 few trees at this time, but noted in them the winter decrease of 

 starch and the increase of oil globules. 



A much greater contribution to the knowledge of the seasonal 

 condition of the stored food of woody plants was made by 

 Russow^ who published his results in 1882. He examined at 

 various seasons the cell-contents of phloem and xylem of stem and 

 root of 92 species, of which 51 species grew in the open at Dorpat 

 in western Russia. The xylem of these trees was not examined 

 in all cases, but, as far as examined, showed starch present in both 

 stem and root in both summer and winter. In the phloem, the 

 variation of starch content was marked, this substance being at a 

 maximum in late autumn, and disappearing from the most of the 

 trees in winter. Examinations were made in two consecutive 

 years, one with a mild winter and one with a severely cold winter. 

 In the mild winter, 10 trees kept considerable starch in the phloem 

 of the stem, but this was reduced to none, or but a trace, in the 

 cold winter. Also, of the 42 species of trees and shrubs kept in a 

 plant house over winter, about a half showed more or less starch 

 remaining in the phloem of the stem. But since nearly a half of 



*( Contribution 126 from the Botanical Department of the University 

 of Michigan. 



This paper is the result of the work of two of my former students 

 under whose names it is published. These two students left me good re- 

 ports of their work, and these reports I have edited and prepared for 

 publication. I should add that a third student, Mr. Nelson F. Macduff, 

 also furnished some of the data. — F. C. NewcombE.) 



^De la Repartition de 1' Amidon dans les Rameaux des Plantes ligneuses. 

 Bull. Soc. de France. XXVI, 1879, P- XLIV. 



'Ueber den Inhalt der parenchym. Elemente der Rinde. Sitzber. Na- 

 turforsch. Gesellsch. Universitat Dorpat. VI, 1882, 369. Abstract in 

 Bot. Centralblatt. XIV, 1883, 271. 



