MACDOUGAL AND SPOEHR— GROWTH AND IMBIBITION. 329 



glass arranged to rest its apices on the three disks. The vertical 

 swinging arm of an auxograph was now adjusted to a shallow socket 

 in the center of the glass triangle while the pen was set at zero on 

 the recording sheet. Water or a solution being poured into the dish, 

 the course of the swelling was traced, the record showing the aver- 

 aged result of the action of the trio of specimens (see Fig. 7). That 

 the amount of imbibition depended upon the presence of certain 

 recognizable substances was demonstrated by the fact that dried 



Fig. 7. Auxograph arranged for recording changes in thickness of trio 

 of cyHndrical sections of Opuntia. The vertical arm, which is set in position 

 on horizontal arm to give a magnification of twenty, rests on a triangle of 

 glass laid on top of the sections. The dish containing the sections rests on 

 an iron cylinder to secure stability and a weight is placed on the T base of 

 the instrument. The record sheet is ruled to millimeters (not shown) with 

 heavier horizontal lines i cm. apart. The heavy curved lines shown repre- 

 sent four hour intervals. The space is ruled to fifteen minute intervals (not 

 shown). Height of clock and lever supports adjustable. 



and dead disks gave proportionate differences equivalent to those 

 shown by freshly cut and living material. 



