174 BOTANICAL GAZETTE [AUGUST 
species. The proportion by weight of powder and oil was the same 
in every case. These were kept at room temperature, and once a 
week a bottle of each species was taken, the oil was removed from 
the powder by filtration and was titrated against N/1o sodium 
hydroxide. The fate of increase of acid measured the strength 
of the lipolytic action and hence, probably, the amount of lipase. 
Results showed the ferment to be most abundant in the leaves of 
those species in which fat was commonest in the stems in winter. 
To determine the exact method by which these seasonal changes 
in the food reserve are effected, however, is beyond the scope of the 
present paper, the purpose of which is to emphasize the important 
part evidently played by the minute anatomy of the stem and root 
in determining the ease of diffusion of water or solutions through- 
out their tissues and thus affecting the character, distribution, and 
seasonal alterations in the stored foods, and doubtless in other 
functional activities of the plant. We may point out that in any 
such physiological problem as this one a thorough knowledge of 
the structures concerned is absolutely essential before sound con- 
clusions can be reached. 
Summary 
1. Previous observations upon the character, distribution, and 
seasonal changes of the food reserves of woody plants in temperate 
regions were in general confirmed by the present investigation and 
were considerably extended. 
2. Astudy of the minute distribution of the food reserves in the 
tissues of the stem (twigs and young branches) during the winter 
shows that (1) starch is commonest in regions remote from centers 
of conduction and in cells with thick, well lignified, small-pitted 
walls; and (2) fat is most abundant in and near the phloem, close 
to vessels, and in cells with thin or unlignified walls or large pits. 
3. These facts indicate that the character of the food reserve 
in any cell depends primarily upon the ease with which water or 
substances carried by water have access to the cell. Where the 
movement of liquids is apparently slow and difficult, the reserve 
persists as starch; where such movement is easy, starch disappears 
at the beginning of winter and fat is produced. 
