Lecture 4 — 97 — Movement and Distribution 



An experiment in this laboratory with squash 

 plants illustrated the relation between the initial in- 

 ternal status of the plant and the external environ- 

 ment during the experimental period. Measurements 

 were made by Stewakd of growth increments in leaf 

 areas occurring during the absorption period. The 

 largest accumulation of salt took place in those leaves 

 of the high salt plants that increased most in area. 

 These were the leaves on the plants in the light. In 

 the low salt plants marked additional accumulation of 

 salt occurred in the leaves in the dark, which, how- 

 ever, increased in area even under these conditions 

 unfavorable for growth. The suggestion appears that 

 the leaves, like the roots, of plants low in salt and 

 high in sugar, maintain for a limited period a rela- 

 tively high salt accumulating capacity, which is not 

 immediately dependent on photosynthetic processes.* 



Still another aspect of salt movement with a def- 

 inite bearing on some of the questions raised above 

 has been usefully studied by means of radioactive 

 isotopes. This is the problem of the movement of 

 ions to developing fruit of the tomato plant (Arnon, 

 Stout and Sipos, 1940) . Large plants were grown by 

 water culture technique and the experiment was begun 

 at a time when the plants bore many fruits at different 

 stages of growth, from small green fruits to large 

 ripe ones. Radioactive phosphate was then introduced 

 into the culture solution and translocation of this newly 

 added phosphate followed by means of a Geiger- 

 Miiller counter and by radio-autographs. After an 

 initial period, the greatest accumulation of the newly 



♦Extensive experiments have been conducted in England 

 by F. C. and A. G. Stew^ard on cucurbits and on certain woody 

 species, with reference to the factors of metabolism involved 

 in the movement of inorganic solutes into leaves and growing 

 points, with special consideration also of anatomical factors. 

 The reports have not yet been published because of war con- 

 ditions and while the writer is privately informed of these 

 researches, it would not be appropriate to anticipate their ^-^^i/* 

 future discussion, yyv** 



b! LIBRA 



