THE INFLUENCE OF GRAVITY 



79 



It may finally be of interest to give some further data showing 

 that the rate of geotropic curvature of these half stems with an 

 apical leaf attached occurs approximately in proportion with the 

 mass of the leaf. In Fig. 58 the curvature of 3 half stems each 

 with a whole leaf was compared with the curvature of the 3 

 sister half stems each with a reduced leaf. All of the 3 stems with 

 whole leaves had reached about the same curvature as stem a, and 

 therefore this one alone is reproduced here. It was found that 

 h, c, and d had bent approximately in proportion with the mass 

 of the apical leaf attached. 



Fig. 59. — Stem split longitudinally and suspended horizontally, one 'half is 

 entirely defoliated, the other has a leaf attached to the apex. The latter bent 

 rapidly in the usual way, while the half stem without leaf bent only very slowly. 

 Apr. 10 to May 23. 



In Fig. 59 a stem was split longitudinally and both halves were 

 suspended horizontally. One half had a leaf at the apex, while 

 the other half had no leaf. The latter bent very slowly in com- 

 parison with the half which had an apical leaf attached, in 

 accordance with the difference in the mass of material available for 

 growth in the two half stems. It may be stated incidentally 

 that the mass of shoots and roots regenerated by the half stem 

 with a leaf was also considerably larger than the mass of shoots 

 and roots formed in the half stem without leaf. The experiment 

 lasted from Apr. 10 to May 23. 



The experiments with split stems give on the whole less reliable 

 results than those with whole stems. Not only the unavoidable 

 errors in halving the stem, but possibly other variables vitiate 

 the result, e.g., the unequal degree of drying of the upper side of 

 the stem and the resulting inequalities in rigidity of the wood. 



