Variation in the Food Reserves of Trees. 239 



Starch in Twigs and Stems. 



Populus deltoides. — In cortex, phloem and xylem of the parts 

 above grounds ; the starch passes through the phases observed in 

 Denmark by Petersen for Populus tremula and in northeastern 

 France by Mer for Populus sp. That is, in both cortex and stele 

 the starch is at a maximum in autumn, disappears wholly in 

 winter, is regenerated in the early spring, and again disappears in 

 May. Russow, however, found starch abundant in winter in the 

 phliem of P. tremula. 



Tilia americana. — The behavior of starch in the stem of this 

 tree is nearly like that of Populus deltoides, except that in Tilia 

 a small amount of starch may be found in the outer part of the 

 phloem, in the medullary rays of the xylem zone, in the xylem, 

 and in the pith probably at all times in winter. It was not seen 

 in the cortex or phloem in the first half of January, and not in 

 the xylem in the last half of January, but examination each week 

 before and after showed its presence in the respective tissues, and 

 its reported absence was probably due to hasty examination. This 

 result agrees more nearly with the observations of Mer on Tilia 

 sp., and of Russow on Tilia europaea, but differs from those of 

 Fischer, who found no starch in winter in any part of the stem 

 of Tilia parvi folia. 



Salix alba. — The twigs and lo-year old trunk of this tree lost 

 all their starch in January in this region (Ann Arbor, Mich.). 

 Fischer reports Salix babylonica, and Mer and D'Arbaumont 

 report Sali.v capraea as retaining some starch all winter. 



Juniperus virginiana. — By the middle of November the twigs 

 and trunk of this tree up to 12 years of age had lost the most of 

 their starch. By the middle of January the last traces had dis- 

 appeared, the medullary rays retaining theirs the latest. 



Compared with this, the behavior of Juniperus communis is 

 described by Fischer as showing no starch in any part of the stem 

 in winter, except for a trace retained in the xylem. 



Ulmus americana. — In the twigs of this tree, the starch disap- 

 peared from the cortex at the middle of December, but did not 

 wholly vanish at any time from either phloem or xylem of twigs 

 or older trunks, though it was much reduced in both phloem and 

 xylem of these members. 



