19 1 7] LOEB—BR YOPII YLL UM 



39 



experiment was begun June 2 1 and the measurements were 

 i July i. The original length of each piece of stem before 



from 



final 



length could be ascertained by direct measurement. First it was 

 found that the length of the split stems which had been suspended 

 with their cortex above was not altered, as shown in table I. 



TABLE I 



Length of split stems placed horizon- 

 tally WITH CORTEX ABOVE (iN CM.) 



At beginning of experi- 

 ment (June 20) 



At end of experiment 



(July i) 



9.0 



11. o 

 10. o 



14.0 



9.0 

 10.8 



10. o 



13.8 



Obviously no growth had taken place in these halves; there 

 may possibly have been a slight shortening, but if this was the case 

 it was so small that it was within the limits of error of measurement. 



An altogether different condition was found in the other halves 

 of the stems which had been suspended horizontally with their 

 cortex below. Here an increase in length was found in the bent 

 part of the stem, while the apical and basal ends which had not 

 bent were practically unaltered also in regard to length. We 

 designate the apical unbent region A, the central bent region of the 

 stem B y and the unbent basal region C. The measurements of 

 4 stems are given in table II (p. 40). 



It is obvious that an increase in length of 15-20 per cent took 

 place in 10 days in the bent central region of the stem (basally from 

 or around the second node behind the apical leaf), while the unbent 

 basal and apical regions showed no distinct alteration of length. 



Fig. 24 is a photograph of marked whole stems 9 days after the 

 beginning of the experiment. The stems had been suspended 

 horizontally in the jar; all had one apical leaf left. That part of the 

 cortex which was below had stretched, while the cortex above was 

 shortened. The India ink marks were 1 cm. distant and were 

 made at the beginning of the experiment. The photograph shows 

 the change in the position of the marks on the convex and concave 

 sides in the bent region of the stem. 





