30 TRANSLOCATION IN PLANTS 



compete osmotically for water. Wee vers (1923) more 

 recently observed similar wilting of ringed branches 

 bearing leaves which lacked chlorophyll and gives similar 

 explanations for the wilting. 



The fresh weights, dry weights, and sugar contents of 

 these ringed defoliated shoots were also lower than those 

 of the other shoots. It is interesting to note that calcula- 

 tions of the molecular concentrations of sugar, assuming 

 it all to be present as hexose, show that in each treatment 

 only a small part of the freezing-point depression is due to 

 sugar, the ringed defoliated shoots showing the least. 



The failure of solutes to move past the rings in the 

 defoliated shoots might be ascribed to the failure of a 

 transpiration stream to carry them, since no leaves were 

 present to cause such a stream. Of course, the conditions, 

 so far as transpiration was concerned, must have been 

 similar in the defoliated shoots that were not ringed and 

 in which solutes did move ; yet it seemed desirable to deter- 

 mine whether or not a movement of water through the 

 xylem would favor the movement of sugar. To this end a 

 large number of twigs of Ligustrum ovalifolium were 

 ringed as in Fig. 1, Nos. 1 and 2, with the exception that 

 an additional ring was made below the lower group of 

 leaves on each twig as at R' . The leaves at the apex of 

 each shoot would insure a transpiration stream through 

 the xylem, while the leaves at the base, with the ring 

 below them, would insure a carbohydrate supply to the 

 xylem. Starting with shoots lacking stored starch in the 

 xylem, it was found that the cortex, medullary rays, wood 

 parenchyma, and pith became densely filled with starch 

 in the defoliated region of those twigs treated as in No. 1, 

 in which the phloem connection with the leaves was intact ; 

 but the same tissues were completely lacking in starch in 

 those treated as in twig 2, in which the defoliated region 

 was isolated by rings from the leaves both above and 

 below. In both treatments starch was abundant in the 

 leafy parts of the stem. In those treated as in No. 2 the 

 xylem was richly stored with starch immediately below 



