RECENT ADVANCES IN SCIENCE 203 



Atkins (Some Recent Researches in Plant Physiology, 191 6, 

 chap, xi) advanced a coherent theory of winter storage and 

 translocation of carbohydrates, in which he suggested that 

 starch stored in the wood parenchyma is transformed into 

 sugars — sucrose being the chief sugar of translocation — in the 

 spring, and passes into the vessels where a high osmotic con- 

 centration is developed. With the opening of the leaves and 

 the rapid increase in transpiration rate, the quantity of water 

 traversing the vessels is greatly increased, and this results in 

 a corresponding decrease in the osmotic concentration of the 

 carbohydrate solution, which, in fact, is found to be the case. 

 Atkins considers that the carbohydrates manufactured in the 

 leaves reach the vessels by way of the bark, medullary rays, 

 and wood parenchyma. 



Extensive ringing experiments have been carried out by 

 O. F. Curtis {Amer. Journ. Bat., 1920, 7, 101-24), who 

 dealt with a variety of plants, chiefly cut shoots growing 

 in water culture. He set out to investigate the fundamental 

 problem of the path taken by organic food materials in their 

 upward passage through the stem during the spring season of 

 active growth. Atkins considers that the carbohydrates pass 

 through the xylem, an opinion he shares with earlier workers ; 

 but, as this conclusion is based mainly on the continued pre- 

 sence of these substances in the wood, Curtis is inclined to 

 require more direct evidence of actual translocation through 

 the xylem tissue. He lays emphasis on the possibility that 

 these soluble substances may quite easily remain stationary 

 in a tissue in spite of a current of water flowing through the cells 

 containing them, and argues accordingly that the mere pre- 

 sence of sugars in the vessels is not evidence of their habitual 

 conduction through those elements. Curtis found that growth 

 practically ceases in a shoot if a ring of phloem is removed 

 below it, unless the leaves are allowed to remain. On the 

 other hand, if the leaves are detached and no phloem removed, 

 growth, although retarded, is not completely stopped. Inci- 

 dentally it is interesting to note that in some of the " ringed " 

 shoots a strip of phloem was accidentally left intact. These 

 shoots showed considerable growth, thus providing a valuable 

 control showing that the check in growth observed in other 

 cases could not be due to injury. Similar experiments were 

 carried out on dormant shoots just previous to the period of 

 bud-opening. Adequate control experiments were introduced, 

 such as injuring the xylem whilst allowing some phloem to 

 remain, and the results obtained were exactly comparable with 

 those in the previous experiment. Experiments were also 

 conducted with fruiting stems, in which a ring of phloem was 

 removed from the stem below the fruit, and no leaves were 



