INFLUENCE OF GRAVITATION ON POST-EMBRYONIC GROWTH. 529 



Still more easily by taking an entire plant of Yucca or Draccena out of the earth and 

 submerging the apex in a glass vessel full of water, so that the thick rhizomes 

 are directed upwards. Even in this case, and under the influence of light, the changes 

 described take place, and after all that has been said, they cannot well be ascribed to 



Fig. 344.— yucca g:loriosa. a a rhizcme ; * stem ; cleaves at apex ; rf subterranean leaf-shoots 

 from the basal part of the rhizome ; ä' leaf-shoots from tlie terminal buds of two shoots of the 

 rhizome; ir c soil of pot /y'; ^^, /; /i the wooden support for the inverted plant ; ia new root ; 

 /• and i new buds of the rhizome. The roots are omitted in the figure. 



any other influence than that of gravitation, although it is at present quite impossible 

 to form any clear idea whatever as to the way in which this influence leads to the 

 final result described. We are here simply in the same position as with almost all 

 the efi"ects of light and gravitation, pressure, injury, and other external influences : 

 [ 3 ] ji m 



