290 TRANSACTIONS OF THE [Sess. lxxviii. 



the whole stem is in a state of elongation. 1 He found 

 that the growing region increased with the activity of 

 growth, and each transverse zone increased to a maximum, 

 and finally ceased altogether as in the root. 



No definite statement is made as to the necessity for 

 repeated measurements on the same plant at definite short 

 intervals or in regard to the possibility or probability of 

 variation under different conditions. 



Pfeffer 2 states that the relation between the regions 

 where growth by cell division and growth by cell stretching 

 are active differs in stems as well as in roots, and the 

 total length of the growing region may also vary con- 

 siderably ; further, that changes must occur whenever the 

 relationship between the vegetative and elongating zones 

 is disturbed by internal or external agencies. 



Thus the length of the growing zone usually increases 

 when growth becomes more active, 3 and also when the 

 stem is etiolated, while the temperature 4 supply of water 

 and other external factors may also influence it. 



The relationship between temperature and the growing 

 region was studied by Askenasy. 5 He found that the 

 growing region was bigger at a lower temperature than 

 at a higher — for instance, larger at 18° than at 27°. 



In the experiments given below the temperature was 

 kept within small limits. 



Some of the problems which suggested themselves at the 

 outset were : — 



I. Do the lengths of the growing regions in roots and 

 shoots of the bean vary regularly or irregularly from day 

 to day under normal constant external conditions ? 



II. Are the growing regions affected by different con- 

 ditions of light and darkness ? 



For instance, does the growing region increase in the 

 dark with the abnormal increase in length of the stem, or 

 does it remain the same ; in other words, is the " rapidity 

 of growth " greater in the dark, or is it due to the abnormal 

 length of the growing zone, as is the case with some 

 climbing plants ? 



1 Sachs, " Flora," 1873, p. 322. 



2 " Physiology of Plants," vol. ii. p. 11. 3 Sachs, loc. cit. 

 4 Askenasy, "Ber. d. Bot. Ges.," 1890, p. 82. 5 Loc. cit. 



