92 TRANSLOCATION IN PLANTS 



was evident after 8 hr. at a distance of 13 cm. above the 

 side twig and 15 cm. below it. In the same time the shoot 

 free in the room whose side twig was 11 cm. long showed 

 lithium had moved up into the tip of the main shoot and 

 backward a distance of 8 cm. A similar backward spread 

 took place when solutions were injected through cuts into 

 the stems of rooted plants. If transpiration was vigorous, 

 the spread was at times more extensive in these rooted 

 plants. 



If leaves were absent below the point of injection, the 

 backward movement of lithium was very slight, only a 

 centimeter or two in 20 hr. if the base of the cut twig stood 

 in water, but if it did not dip in water, lithium was found 

 to have moved backward to the cut surface, a distance of 

 15 to 27 cm. in 20 hr. 



Many experiments were described in detail in which the 

 backward spread of lithium nitrate and eosin solutions 

 were studied in relation to the effects of factors influencing 

 the rate and extent of the backward flow, the extent of 

 tangential spread, the relation of movement to method of 

 introduction, etc. 



In order to determine whether the phloem tissues were 

 adequate in carrying foods, she compared the observed 

 rates of movement of lithium and eosin through phloem 

 tissues with the probable rates at which products of assimi- 

 lation must be carried from the leaves. Assuming that 

 carbohydrate is manufactured by photosynthesis at the 

 rate of 0.5 g. per square meter per hour for 10 hr. during 

 the day, and that the whole of this is transported within 

 24 hr. she estimated that carbohydrate might be expected 

 to be removed from the leaf at the rate of 0.28 g. per hour 

 (actually this figure should have been 0.208, but this mistake 

 is not important for she might as well have assumed a 

 higher rate of photosynthesis). The area of a bean leaf 

 was determined as was also the area of the cross section 

 of a petiole and that of the sieve tubes of the petiole. 

 Using the above figures, she calculated that, from the 

 particular leaf in question, carbohydrates would be removed 



