- 126 — 



no possibility of the hypocotyl reversing its curvature and thus 

 returning to the vertical. If this were so there seems no doubt 

 ihat a corkscrew effect would be produced. It is certain that the 

 region of growth is near the cotyledon, as Rothert showed to be 

 the case ') with Setaria. He marked the hypocotyl at distances of 

 11/2 n^ni and found after 23 hrs. that the average growth of the four 

 zones (beginning with the one next the cotyledon) was 465, 120, 

 28, 5 p. c. in another experiment he got 127, 55, 8 p. c. In acro- 

 petal growth however it is important to know the distribution of 

 growth for shorter intervals of time. We therefore made a series 

 of observations on the growth of Sorghum: the hypocotyl was 

 marked at intervals of about 2 ^nm the distances between which were 

 carefully determined with a horizontal microscope (20 divisions of 

 the micrometer = one millimetre), and again after an interval of a 

 few hours. 



Table I. 



Note: Zone 1 in next the colytedon. 



The results are given in Table I. Under the heading »Time« 

 are given the periods of time between marking the seedlings and 

 re-measuring them. Under the heading »Zone 1«, »Zone 2«, etc., 

 are given the original lengths of the zones and the increase ex- 

 pressed as a percentage. In these columns the length is given in 

 terms of micrometer graduations but in the last columm the original 

 length of the region which has shown decided growth is given in 

 millimetres. The experiments given are selected as typical out 

 of a number of similar trials. It is clear that a region of from 3 to 

 6 mm may at a given moment be growing to a fair amount and 

 that the growth is more evenly distributed than is obvious in 

 Rotherts experiments. These resuUs suggest that reversal of the 



') Cohns Beiträge 7, p. 68. 



