94 



by a velvet collar. A hlac-k canllioard collar. Fig. III. P.C. slips over the 

 bottle and rests iipoii the platform below the bottle. A piece of white card- 

 board on the platform serves as a reflector for the light entei-ing the bottle. 

 It is this (lull red light wliich is carried to the obji-ctive of tlic niicroscope 

 and used to make the readings. This light enters only when making the 

 I'eadings and has not, in the number of cases tried, produced any stimulus 

 that would effect the experinu'ut and alter the response to the ni>i'ni;il light 

 stinuilus. However, I have yet to try experiments on I'halaris. 



The internal construction of the box, Fig. II, consists merely of a ver- 

 tical rod on which works a burette clamp. The rod is so placed that a test 

 tube containing the plant under study can be adjusted easily into position 

 opposite both the iris and the objecti\e of the microscope. The door of the 

 box is fitted with strips of velvet so as to make it light proof. 



To use the apparatus, seedlings are grown in soil, sawdust, etc., in test 

 tubes in the dark room. These culture tubes should always be held in a 

 \ertical position while Ix'ing adjusted in the l)ox for study. The box is 

 "loaded" in the dai-k room and th(^ plants ]»laced so as to be in thi' field of 

 the microscope. The iris is closed and the door of the box is locked. 

 The plant is then brought into focus using the illumination secured by rais- 

 ing the collar, I>('. to a sutticient height and thus ixTmittiiig the reflected 

 light to enter the bottle from below. Readings are taken at intervals of 

 several minutes before opening the iris in oi'der to be cerlain that no geo 

 troi)ic stinuUi other tlian the noi-mal are acting. Wlicn no readings are 

 being taken the collar rests upon the platform. 



The i)lant is then laterally stinuilated by o|iening the iris to any de- 

 sii'ed size for a dehnite leiigtli ol' time. The nnri-or rcliects the light 

 through the iris onto the plant. 



The nucroscope is kept covered at all times with a photographer's focus- 

 ing cloth. .Ml of I he readings are made under this cloth. This ])revents 

 any light Ironi passing thro\igh the microsco]ic .and beisig focused outo the 

 l)lant. 



To record the results ;i gi-a|ihic recoi'd ni.ay he made, using the ordi- 

 nates lo denote Ihc exiciit ol' cnrNjilnre in s|>accs on liic nncrouictcr eyc- 

 jiiece. and Ihc abscissas to denote the lime of stinuilal ion. or presentation 

 period, tiie Latent period, and the length of time foi- the completion of Ihc 

 response. Figure I \' illustrates s\ich a record: 



