THE INFLUENCE OF GRAVITY 



27 



organ in the lowest parts of the organ. The water of the sap has 

 the effect of accelerating the growth in the lower part where the 

 sap collects and this causes secondarily a flow of sap of the whole 

 organ to the lower edge. The inhibition of growth in the upper 

 edge of the organ, therefore, is not a direct effect of gravity but 

 only a secondary consequence. This can be proved by suspend- 

 ing detached leaves sidewise under water but near the surface. 

 In this case a seepage of tissue fluid to the lower edge of the leaf 

 will also occur, but since the upper notches are in water, the rate 

 of chemical reaction in the notches on the upper side of the leaf 



In air 



In water 



la 



Fig. 26. — In leaf I, suspended in air, roots and shoots are formed only in 

 the notches of the lower side of the leaf, while in leaf la, suspended in water, 

 this directive influence of gravity does not exist, inasmuch as roots and shoots 

 are formed on both the upper and the lower sides of each leaf. Only the leaf 

 suspended in air shows the red pigment indicated by stippling. Oct. 26 to 

 Dec. 15. 



will not be slower than in the notches of the lower side of the 

 leaf. Figure 26 shows such an experiment. Leaf I was sus- 

 pended sidewise in air and roots and shoots formed in the lower 

 notches exclusively. The sister leaf la was suspended sidewise 

 under water near the upper surface of the water. In this case 

 the influence of gravity disappeared completely since the forma- 

 tion of roots and shoots in the upper notches was as plentiful as 

 in the lower notches. 



It seems as if it were necessary to distinguish in the plant 

 between the liquid enclosed in vessels (resembling the blood and 



