METHOD OF PERFORATION 



341 



0-6 mm., and of positivity at a corresponding point on the 

 opposite side. 



Table XXIV. — Showing Distribution of Geotropic Excitability 



THROUGH the StEM OF BrYOPHYLLUM (DIAMETER =3-6 MM.). 



After the electric test, transverse sections of the stem 



were made at the radial line of the passage of the probe. 



Thus, in a particular experiment 



with Bryophyllum, the point of 



maximum geo-electric response 



was found to be at a distance of 



0-8 mm. from the surface. By 



means of the micrometer-slide on 



the stage of the microscope and 



the micrometer eye-piece, the layer 



0-8 mm. from the surface was 



examined ; this sensitive layer S 



was recognised as the continuous 



* starch-sheath ' or endodermis 



containing unusually large-sized 



starch-grains (fig. 204). These 



often occurred in loosely cohering 



groups of 8 to 10, and their 



appearance is very different from the small-sized irregularly 

 distributed grains in other cells. 



In all the specimens examined, the experimentally 

 located geo-perceptive layer was found to coincide with 



Fig. 204. Transverse section 

 of the stem showing contin- 

 uous geo-perceptive layer 

 s ; enlarged view, s', of cell 

 of endodermis containing 

 group of large starch-grains 

 (Bryoph3'llum). 



