384 



INFLUENCE OF GRAVITY ON ARRANGEMENT OF ORGANS 



We have stated in a preceding paper- that the sap from a leaf flows 

 normally into the stem and that this is the reason of the inhibitory 

 or retarding influence of the stem upon root and shoot formation in a 

 leaf of Bryophyllum. This idea is supported by the fact that when 

 a piece of stem is left in connection with a leaf suspended in moist air 

 no collection of red or purplish pigment occurs in the leaf but that 



Fresh stem 



Upper side 



Fig. 9. Showing the distribution of the purple pigment in the stem. 



it is found in the petiole, in the stem, and in the new shoots which are 

 formed by the stem. This is illustrated by Fig. 8. The leaf on the 

 right was left in connection with a piece of stem, while the sister leaf 

 (to the left in Fig. 8) was detached from the stem. The latter shows 

 a collection of the pigment in the vessels near each notch from which 

 roots and shoots develop and the new shoots are full of the pigment. 

 The sister leaf in connection with a piece of stem (to the right in 



2 Loeb, J., /. Gen. Physiol, 1919-20, ii, 297. 



