MACDOUGAL AND SPOEHR— GROWTH AND IMBIBITION. 333 



Fig. 8. Auxographic tracings of swelling of cylindrical sections of 

 Opiintia Sp. — joints formed in 1915. A compound lever set to magnify 

 swelling 20 times carries a pen downward from the zero line on a sheet 80 

 millimeters in width, carried past the pen in 24 hours. The right hand or 

 upper line a was traced by a trio of sections of an average diameter of 13 mm. 

 which showed a swelling of 50/20 ==2.5 mm. in hundredth-normal sodium 

 hydrate, which was 19.2 per cent, of the original. The lower line c was traced 

 by a trio of sections of an average diameter of 13.8 mm. in hundredth-normal 

 hydrochloric acid which showed a swelling of 2.55 mm. or 18.5 per cent. The 

 middle line was traced by a trio of sections of an average diameter of 12 mm. 

 which swelling 2.55 mm. or 21.3 per cent. Feb. 22, 1917. (Upper half of 

 figure.) Reduced J4. 



Auxographic tracings of old joint of Opiintia blakcana. The upper right 

 hand line a was traced by swelling of trio of sections of an average diameter 

 of 10 mm. in hundredth-normal sodium hydrate. The increase was 3.6 mm. 

 or 36 per cent. The middle line h was traced by the swelling of a trio of 

 sections of an average diameter of 11 mm. in distilled water. The swelling 

 was 3.6 mm. or 32 per cent'. The lower line c was traced by the swelling of a 

 trio of sections with an average diameter of 10 mm. in distilled water. The 

 swelling was 3.5 mm. or 35 per cent, of the original. A notable difference 

 between the rates of swelling in- the three solutions is exhibited in contrast 

 wath those of the series of joints of 191 5. (Lower half of figure.) Reduced K'. 



crease or decrease in the water-absorbing capacity of the colloidal 

 substratum of the cell. At the same time the degree of imbibition 

 and of swelling plays an exceedingly important part in metabolism 

 and hence in the formation of plastic material necessary for growth 



