330 MACDOUGAL AND SPOEHR— GROWTH AND IMBIBITION. 



The auxograph used in making the measurements represents an 

 modified form of an apparatus originally designed by the senior 

 author in 1901. The improved instrument consists of a compound 

 lever, the components of which are suspended in adjustable bearings 

 held in the arms of a metal support of " Y" form with the arms of 

 unequal length. One free arm of the bearing lever is forked, the 

 upper segment carrying a counterpoise which may be moved to give 

 any desired pressure on the bearing contact with an object the 

 swelling of which is to be' measured. The lower segment of the 

 free part of the bearing lever has a sleeve with a short socket 

 hinged to its lower side. A thin glass rod set in this socket extends 

 downward to a length of a few centimeters and rests in a concavity 

 in the center of a glass plate laid on the trio of sections in a suitable 

 small glass dish. The sleeve may be moved along the lever to give 

 a magnification between ten and fifty to a pen carried by the other 

 free lever arm. The two small levers are connected by a short 

 length of jewelers' chain in such manner as to minimize friction and 

 other sources of error. The pen is arranged to bear on a slip of 

 paper 8 cm. wide ruled to millimeters and it is carried by a cylin- 

 drical clock which gives it a movement of 28 cm. in 24 hours. The 

 compound lever was supported by a rack and pinion column which 

 made it adjustable through a range of 12 cm. in height. 



The clock may be moved vertically on its support and fastened 

 at any height by a set screw. The delicacy of this apparatus was 

 such that it could not be operated on a wooden table in an ordinary 

 room. Cement, stone or brick piers with a slab of slate, wood or 

 stone furnished the necessary steadiness. The dishes in which the 

 sections were immersed in swelling solutions were placed on top 

 of iron cylinders 15 cm. high and about 8 cm. in thickness and the 

 dishes were held in place by clay luting. A weight of about 4 or 5 

 kg. placed on the " T " base of the instrument completed an arrange- 

 ment by which it was possible to secure undisturbed records of 

 swelling of sections of cactus, of plates of colloids, and also of 

 growth of joints of this and other plants. 



The following measurements of the swelling capacity of sec- 

 tions from the terminal joints were secured in 1916 and 1917. One 



