378 



INFLUENCE OF GRAVITY ON ARRANGEMENT OF ORGANS 



weight of the lower half of such an organ is always greater than the 

 dry weight of the upper half; while when an organ forms shoots and 

 roots on both the upper and lower side {e.g. a leaf suspended vertically 

 and sidewise in water) no such difference in the dry weight of the 

 upper and lower half should be expected. Determinations made by 

 the writer confirm this expectation. 



These experiments were carried on in the following way, A num- 

 ber of leaves were suspended vertically and sidewise in an aquarium 



TABLE I. 



Dry Weight of Upper and Lower Halves of Leaves Suspended Vertically and Side- 

 wise in Air. Roots and Shoots on Lower Side Only. 



filled with moist air. The majority of these leaves formed roots in 

 abundance on the lower side but not on the upper side. For this 

 experiment leaves with perfect symmetry were selected. After 

 about 4 or 5 weeks a number of such leaves were cut as accurately as 

 possible along the middle rib and the fresh and dry weights of the 

 upper and lower halves were determined. The dry weight of roots 

 and tiny shoots formed on the lower side was included in the dry 

 weight of the lower halves of the leaves. The lower halves of the 

 leaves had, without exception, a higher dry weight than the upper 

 halves (Table I) . 



