90 TRANSLOCATION IN PLANTS 



and Prunus padus, in which lithium nitrate was introduced 

 through a small side twig which was cut off, or through a 

 cut petiole, it was found that, though lithium had pene- 

 trated throughout the transpiring shoots within a few 

 hours where the phloem had not been separated from the 

 wood, it had, even after 3 days, moved a distance of only 

 3 to 4 cm. into the phloem where this was separated from 

 the xylem. 



Other attempts were made to force solution through the 

 phloem tissues by dipping strips of phloem attached to 

 the base of leafy shoots into solutions of lithium nitrate, 

 but in from 25 to 30 hr. the lithium had moved a distance 

 of only 2 to 3 cm. There was little difference in movement 

 between those from which there was rapid transpiration 

 and those with slow transpiration, in fact the latter showed 

 slightly greater movement. When pieces of xylem were 

 cut out and the exposed phloem was protected from drying 

 by enclosing in a glass tube closed with ''plastilina," 

 lithium did not pass the operated region if the length of 

 xylem removed exceeded about 2 cm. With 2 cm. of 

 xylem removed some diffused through the phloem and 

 was carried above for 8 to 15 cm. after 20 to 32 hr. The 

 leaves in these cases became wilted. The movement here 

 seemed, however, to take place through the xylem for in 

 other experiments in which crystals of the salt or a strong 

 lithium nitrate solution (1 M) were not introduced into 

 cut xylem but were placed on a leaf or on the cortex of the 

 stem, from which the epidermis and periderm were removed, 

 the inward moving lithium traveled only 1 to 2 cm. if 

 transpiration was prevented but extended 10 to 40 cm. 

 when transpiration was not prevented. 



Experiments were also carried out to determine the 

 ability of phloem tissues to absorb water and solutions. 

 These showed that the amount of water absorbed through 

 the phloem was only one two-thousandths to one one-thou- 

 sandth that absorbed through the xylem. 



All of these experiments led her to conclude that trans- 

 location through the phloem is extremely slow, whereas 



