THE METHOD OF MOVEMENT 221 



through the phloem was strongly urged by Lecomte 

 (1889) and has been fairly generally accepted by botanists 

 since the work of Czapek (1897). He demonstrated that 

 the killing of the petiole with steam or chloroform pre- 

 v^ented the removal of carbohydrates from the leaves. He 

 used the test for disappearance of starch as a criterion 

 for removal. This, of course, is not always a conclusive 

 test especially when used with leaves, yet under the 

 conditions of Czapek's experiments seems to have been 

 suitable. Deleano (1911), although he found that killing 

 of the petiole with steam or chloroform distinctly retarded 

 carbohydrate removal from the leaf blade, reducing it to 

 one-third the normal, claimed that there was still a fairly 

 rapid backward translocation through the dead petiole. 

 His criterion for loss, however, was based on a change in 

 dry weight or sugar content of the blade expressed as a 

 percentage of the fresh weight. He assumed that the 

 fresh weight of the attached and darkened leaf remained 

 constant over a period of 26 to 48 hr. and that any change 

 in dry weight expressed as a percentage of this fresh weight 

 was a real change in total dry weight. In one experiment, 

 for example, he found in the normal leaf a reduction of 

 3.49 per cent in dry weight expressed in this manner. 

 It is probable, however, that much if not all of this change 

 in percentage was due to an increase in water content of the 

 darkened leaf and not to transport of solids. It is sur- 

 prising how frequently a change in percentage compo- 

 sition is assumed to be due to a change in one constituent 

 when the change in amount of any one or more of sev- 

 eral other variables may have been responsible (see also 

 Sec. 12, pp. 64-67). More recently, however (see especially 

 Deleano and Andreesco, 1932), Deleano has published 

 several papers dealing with movement of various nutrient 

 elements including nitrogen, into and out of leaves of 

 Salix fragilis, and has expressed the data on an absolute 

 basis. For most of the mineral elements he has found 

 that they increase until about June 1, remain practically 

 constant until about Sept. 1 to 20, and just before leaf 



