204 SCIENCE PROGRESS 



allowed to remain on the section of stem above the ring. The 

 results obtained were identical with those recorded by Hanstein 

 in i860 — namely, cessation of growth in the fruits above the 

 ring. Moreover, Curtis was able to show, by dry weight and 

 volume measurements, that the fruit gained nothing but water 

 from the date of ringing. The author concludes that either 

 the xylem carried no essential food material, or alternatively, 

 whilst the xylem may carry some, the phloem carries the im- 

 portant constituents, e.g. possibly nitrogenous compounds. 



In the cases where leaves are allowed to remain on a ringed 

 shoot, their photosynthetic activity in some degree compensates 

 for the loss of food material normally carried by the phloem ; 

 as is shown by the considerable growth of the shoot under 

 these conditions. In addition, the osmotic concentration above 

 the ring is found to be greater in the presence than in the 

 absence of these leaves, additional evidence of the part they 

 play. Curtis completed his case by employing several different 

 methods to extract and estimate the carboh^^drates of his 

 ringed shoots, and was able to supplement the results of his 

 growth measurements by showing that carbohydrates could 

 not pass a gap in the phloem of the stem, either upwards or 

 downwards. Perhaps the most striking result obtained is in 

 the case of the sugar maple, Acer saccharuni, which bleeds sugar 

 solution when it is tapped, yet does not remove its carbo- 

 hydrates from the xylem of a length of stem when the path 

 through the phloem has been interrupted. 



Winter storage of nutrient materials has been studied by 

 E. W. Sinnott {Botanical Gazette, 191 8, 16, 162-75) from the 

 anatomical standpoint. Previous investigations on the rela- 

 tion of anatomical structure to the nature of the stored food 

 materials have resulted in the broad classification of trees into 

 starch-storing and fat-storing, the former retaining starch in 

 wood and pith throughout the winter, and the latter replacing 

 starch by fat in all its tissues in the autumn. From examina- 

 tion of a large number of species, Sinnott is able to confirm in 

 general the results obtained by other workers, but finds that 

 the line of distinction between " starch trees " and " fat trees " 

 is not well defined, many types storing both starch and fat in 

 large quantities. A study of these cases convinced the author 

 that the character associated with starch storage was a thick 

 or unpitted cell wall, whilst fat was accumulated in cells with 

 thin or much pitted walls. This fact, together with the posi- 

 tion of " fat cells " in close proximity to water channels, led 

 to the suggestion that it is a question of the conversion of 

 starch into fatty materials, a process which appears to be 

 dependent upon easy access to the water, or possibly to 

 enzymes in the water of the vessels. Some co-ordination of 



