284 



INTRODUCTION 



[Ch. X. 



we find during a period of 20 hours little growth occurring at 

 the root tip, a maximum of growth at 3 or 4 millimeters from 

 the tip, and further up less growth, until a zone of almost no 

 growth is reached. 



An analysis of the substance of the stem at different levels 

 below the tip reveals the same thing — a sudden increase in the 



amount of water 

 from 73% at the 

 tip to 88% at the 

 first internode (II), 

 reaching a maxi-^ 

 mum at 93% in the\ 

 second internode 

 (III), then falling 

 slightly (92.7) to 

 the fifth internode 

 (VI, Fig. 77). The 



Fig. 77. — Curve shOTving the percentage of water in suc- 

 cessiye internodes of hothouse plants of Heterocen- 

 tron roseum Hook, et Arm., ahout 4 decimeters high. 

 The ordinates indicate the percentage of water at experiments and ob- 

 each internode from the terminal bud (I) to the fifth „„„,,„i-„„ nT^„T. 



(VI). (From Kbaus, '79.) servations upon 



which these conclu- 

 sions rest thus agree in assigning the chief role to water in the 

 growth of plants. 



While the fact that water constitvites a large proportion of 

 the growing animal was made known by the classical researches 

 of Baudeimont and Maetin Saint-Angb ('51), the impor- 

 tance of the part which it plays in the growth of animals seems 

 first to have been appreciated by Loeb ('92, p. 42), who 

 showed how in the withdrawal of water by plasmolytic meth- 

 ods growth was interfered with. Later I made a series of 

 determinations of the relative part played by water and dry 

 substance in the growth of an animal (tadpole). Eggs and 

 embryos at various ages were weighed after removal of super- 

 ficial water. Then they were kept in a desiccator from which 

 air had been pumped and which contained a layer of sulphuric 

 acid to absorb moisture. After repeated weighings a condition 

 was found in which the drying mass lost no more water (con- 

 stant weight). The total diminution in weight indicated the 

 mass or volume of free water contained in the organism at the 

 beginning of the experiment. Numerous weighings were 



