4«8 



LIFE MOVEMENTS IN PLANTS 



passage of the pi'obe. Thus in a particular experiment with 

 Brijophyllum the point of maximum geotropic excitation 

 was found to be at a distance of 0*8 mm. from the surface. 

 By means of tlie micromoter slide in the stage and the 



micrometer eye-piece, the 

 internal layer OvS mm. 

 from the surface was 

 examined ; the particular 

 sensitive layer S was re- 

 cognised as the continu- 

 ous 'r^tarch sheath' or 

 endodermis containing 



unusually large sized 

 starch grains (Fig. 17(»). 

 These often occurred in 



PitJ. 17(5. — Traii8ver?e section showing con- 

 tiiiuoii8 geo-perceptive layer S : enlarged view loOSCly Cohering groups 

 S' of cell of endodermis containing group of of 8 tO 10 particles, and 



large starch grains. {Bn/ophyihrn). their appearance is very 



(lifferent from the snia'l 

 si/.etl irregularly distributed grains in other cells. 



Examination of the microscopic section of the Hower 

 stalk of Nymphcea shovved that the 'starch sheath' was not 

 continuous but occurred in crescents above the vascular 

 bundles which are separated from each other. The occasional 

 failure of electric detection of the perceptive layer is thus 

 due to the probe missing one of the crescents, which with 

 intervening gap.-', are arranged in a circle. 



I give below a number of experimental determinations 

 of the geo-perceptive layer in difl'erent s[)ecimens together 

 with the micrometric measurement of the distance of the 

 'starch sheath' from the surface, the transverse section 

 being mads at the place where the probe entered the shoot. 



