-l^' 



46 JOSHUA ROSETT 



As growth proceeds, the upper layer of the medium becomes 

 thin and about the color of port wine. The salt is dissolved in 

 the water taken up by the osmotic sac, and propelled upwards 

 to the growing tip of the stem. There part of the salt in solu- 

 tion is used up in growth, and the remaining dilute solution 

 is set free and, partially reduced, rises to the top of the medium. 



INFLUENCE OF INTERNAL AND EXTERNAL CONDITIONS 

 UPON THE RATE OF GROWTH 



The stem varies in thickness from 0.24 to 0.12 mm. The diam- 

 eter of its lumen is from 0.08 to 0.04 mm. The height of 

 the stem depends upon the total amount of KMn04, upon the 

 height of the column of liquid within the container, and upon 

 the amount of water available for bringing the salt into solu- 

 tion within the osmotic sac. For some time it seemed impossible 

 to grow stems taller than about 38 cm. Upon investigation it 

 was found that after some hours of growth the osmotic sac, 

 resting upon the bottom of the vessel, became surrounded by 

 a highly concentrated zone of the colloid solution. Water had 

 been taken up by the sac from the solution immediately sur- 

 rounding it, and, the supply of water having become exhausted, 

 growth of the tube above had been stopped. This condition 

 was obviated when the crystal was supported at some distance 

 above the bottom of the vessel. The concentrated zone of the 

 colloid solution being of a higher specific gravity, then sank to 

 the bottom and was replaced by fresh solution of a lower specific 

 gravity. Specimens have thus been grown nearly 2 meters 

 high, in glass tubes, as has been mentioned. 



The rate of elongation of the stem is greatly influenced by 

 temperature. Chemical processes are more active, and the 

 osmotic pressure of a substance in solution increases, as the tem- 

 perature rises. These facts partly explain the relation. Thus 

 while growth is more active at the tip of the stem with every rise 

 in temperature, a greater supply of KMn04 is at the same tim6 

 furnished by the increased osmotic pressure of the KMnO, solu- 

 tion within the canal of the stem and the osmotic sac. At a 

 temperature of 0°C. the stems grow at the rate of 2.5 cm. in 



