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NOTE ON CURVATURE OF CUT STEMS OF 

 BRYOPHYLLUM CALYCINUM 



BY 



P. F. Fyson and K. Venkataraman, 

 Presidency College, Madras. 



Loeb in 1917 published (l) the results of a series of experiments 

 on curvature induced in cut stems of Bryophyllum calycinum, sus- 

 pended in moist air by threads, one at each end. He found, and 

 published figures in support, that curvature, apparently due to gravity 

 took place, whether leaves were left attached to the plant or not ; 

 but much more strongly so, when a leaf near the apical end was left, 

 than when all but a basal leaf were removed. He also found that 

 roots were formed adventitiously, on that region only where the 

 curvature was a maximum, and that root-formation was strongest, 

 when an apical rather than a basal leaf was left. From this, he drew 

 the conclusion, that special root-forming and curvature-producing 

 substances (hormones) are manufactured in the leaf, and passed down- 

 wards, but not upwards, along with the products of assimilation. 



The experiments described here, were made to test these facts and 

 deductions on plants growing in Madras. Healthy stems of Bryophyl- 

 lum calycinum were used and straight pieces 6 to 8 inches long were 

 cut, and in every case the apical bud and the first visible internode, 

 were removed to prevent continued growth, as was done by Loeb. 



All the leaves were removed except one or both apical leaves or, 

 one or both basal leaves, and the pieces suspended over water in a glass 

 chamber. No particular difference was observed, which could be cor- 

 related with the presence of one or both leaves, whether at the base or 

 apex: But those with one or both apical leaves curved more than 

 those with basal. (Plate I, figs 1, 2 and 3) Loeb in explaining this as 

 due to the formation of geotropic hormones in the leaf and their pass- 

 age always down the stem, appears to have overlooked the possibility 

 of the curvature being induced by weight, for no attempt apparently, 

 was made to eliminate this. We found however, that if a third thread 

 was used to support the piece at its centre of gravity or if the pieces 

 were laid on a flat board (fig. 11) no curvature took place. (Compare 

 in Plate I, figs. 8, 9, 10 with 5, 6, 7.) 



In order to support the piece without introducing other factors, 

 we attached to the piece near its centre of gravity a fine thread, which 

 after passing over a pulley, supported a pan, in which weights were 



