14 TRANSLOCATION IN PLANTS 



or anything other than sugar were acting as a Umiting 

 factor for the growth above the ring, one would not expect 

 the starch to disappear, yet the shorter the piece above the 

 ring, the earlier was the disappearance of starch, and the 

 sooner did growth practically cease. 



Similar results were obtained with all the plants experi- 

 mented with including Acer saccharum, A. rubrum, Fagus 

 grandifolia, Pyrus communis (pear) Pyrus malus (apple), 

 Crataegus sp., and Ostrya virginiana. Detailed data from 

 several of these experiments are given in an earlier paper 

 (Curtis, 1920a). All of these plants store an abundance of 

 starch in the xylem tissues and some of them {A. saccharum, 

 A. rubrum, and Ostrya) contained an abundance of soluble 

 sugars in the xylem at the beginning of the experiment, 

 and yet the xylem did not seem capable of carrying these 

 solutes longitudinally in sufficient abundance to allow for 

 normal shoot growth. 



5. Disappearance of Starch below Rings and Results 

 from Double-Ringing. — Hartig's experiments (1858) are 

 often cited as proving that carbohydrates are carried 

 upward in the transpiration stream. He found that, when 

 a tree was ringed, the starch below the ring disappeared. 

 He therefore assumed that it must have moved up through 

 the xylem, for the phloem connections with the top were 

 severed. Selecting young oak trees of about the diameter 

 of one's arm he ringed them at intervals of eight days from 

 Apr. 1, 1857, until the middle of September of the same 

 year. The rings were 2 in, broad and placed 4 ft. from the 

 ground. Examination the following spring showed that 

 all the starch below the rings in those trees ringed previous 

 to June 3, 1857, had disappeared while those ringed after 

 that date still contained starch; but it disappeared from 

 these also by the autumn of 1858. At the time of ringing 

 he also cut down a few trees. The following year the starch 

 had disappeared from the roots of a number of these felled 

 trees also, but since the roots of some of them still contained 

 starch, he concluded that in the ringed trees the carbo- 

 hydrates stored in the roots must have been carried up with 



