386 INFLUENCE OF GRAVITY ON ARRANGEMENT OF ORGANS 



4. It was, however, still necessary to prove the idea that gravity 

 causes sap to collect in larger quantity in the lower parts of organs. 

 This gap is filled by the present paper in which it is shown, first, that 

 in the leaves suspended in moist air a red pigment is formed which 

 has a tendency to collect gradually in the lowest parts of the leaf 

 when the latter is suspended in a vertical plane. This red pigment 

 serves as an indicator for the distribution of sap in the leaf and thus 

 shows directly the tendency of the sap to collect in greater abun- 

 dance on the lower edge of a leaf suspended in a vertical plane. 



Second, it is shown that when leaves or stems of Bryophyllum are 

 suspended, in the way described, under water instead of in moist air, 

 roots develop on the upper side as well as on the lower side. The 

 directive effect of gravity upon the arrangement of organs disappears 

 in this case since the abundance of the outside water makes the 

 effect of a slight difference in the distribution of sap between the 

 upper and lower side a negligible factor. 



Third, it is shown that the dry weight of the lower half of leaves 

 suspended sidewise for several weeks in moist air in a vertical plane 

 is greater than that of the upper half when roots and shoots are 

 formed on the lower side only. This indicates that material from 

 the upper half flows into the growing organs of the lower half. No 

 such difference between upper and lower half of leaf is found when 

 the leaves are suspended in the same way in water and roots and 

 shoots are formed on both sides of the leaf. 



5. It is shown that when a leaf connected with a piece of stem is 

 suspended in moist air the red pigment goes into the stem instead 

 of collecting in the lower part of the leaf, thus supporting the view 

 expressed in a preceding paper that the inhibitory action of the stem 

 on the root and shoot formation in a leaf of Bryophyllum is due to the 

 fact that the material available in the leaf for organ formation is 

 naturally sent into the stem. 



