LOCALIZATION OF THE SENSORY ZONE 129 



bored in two sides and the top and rubber tubes inserted and 

 fastened in a curved position in such manner that ventilation is 

 secured without the admission of light. After the chamber has 

 been made, take it into a dark room, close the opening in the door 

 by means of a stopper, and put a piece of photographic paper in- 

 side. Set in direct light for an hour, then examine paper in dark 

 room and note if it has been acted upon by light. 



When the seedlings have been placed in the box it should be 

 set in an exposed position with a mirror or heliostat arranged to 

 throw horizontal rays into the opening. After five hours open 

 and note positions of cotyledons. Those covered by the tinfoil 

 will have made but little curvature, while the normal specimens 

 will show a noticeable curvature toward the light. 



FIG. 65. Phototropic chamber. A, tube admitting light which passes through the 

 flask B, containing colored liquid. , E, cleats with packing on outer faces against 

 which the door closes tightly, and is held by the bolt F, which is pushed through a 

 hole at D and secured by a nut. ff, /, ventilating openings. M, opening which 

 may be closed with ordinary stopper, or receive a second tube. 



Repeat this experiment with seedlings of Phalaris Canariensis. 

 Next cover the basal portions of another set of seedlings by 

 cylinders of tinfoil or black paper and compare results. It may 

 be seen that the region of the tip alone is sensitive to light and 

 that when this is covered no reaction occurs. The region of ex- 

 treme sensitiveness does not include more than about 3 mm. of 

 the tip of the cotyledon. 

 10 



