MOVEMENTS OF GROWTH. 393 



small seeds, or from seeds robbed of one of their cotyledons. The 

 measurements of the different parts of the plant are easily made. 

 The stock of reserve material in bean-seeds is very large, so that 

 the first stages of germination in my experiments could, in all 

 cases, proceed normally. At a later stage, although assimilatory 

 activity was not excluded, a considerable difference in the growth 

 of the plants became apparent, and this could only be referred in 

 the main to the more or less considerable stock of reserve material 

 in the cotyledons of the seeds. 



159. The Quantity of Water in Plants and their Growth. 



Normal growth of the cells is only possible when they contain 

 an adequate quantity of water. This fact is easy to understand 

 from various considerations. Here it need only be pointed out 

 that active growth presupposes energetic turgor-extension of the 

 cells, which again is only possible when the tissues are rich in 

 water. If the turgescence of the cells sinks, owing to loss of water, 

 their rate of growth also at once diminishes. We germinate 

 maize, pea, or bean seeds in sawdust. When the roots have 

 attained a length of a few cm., we make fine ink-marks on them 

 at a distance of 2 cm. from their tips, and fix the seedlings in 

 suitable glass vessels in the manner indicated in 154. These 

 vessels we fill with different fluids ; one with spring water, a 

 second with a 0'5 p.c. solution of Potassium nitrate, a third with 

 a I/O p.c. solution of the same salt, and a fourth with a 2 - p.c. 

 solution of it. The roots must reach vertically downwards into the 

 fluids. At the end of twenty-four or forty-eight hours we deter- 

 mine the amount of growth which the roots have experienced. In 

 each case we employ three or four seedlings, and take the average. 

 It is found that the roots in contact with spring water grow the 

 most actively. With increasing concentration of the Potassium 

 nitrate solution, however, their growth becomes less vigorous, from 

 fche fact that the solutions are now able to remove water from the 

 cells, and consequently reduce their turgescence. In fairly concen- 

 rated solutions of saltpetre (e.g. 10 p.c. solutions) the roots do 

 not grow at all. Indeed, they become shorter since they pass into 

 a state of plasmolysis. 1 



It is remarkable that fungi continue to grow in fluids whose 

 concentration is much too great for the growth of higher plants. 

 We prepare a solution containing in every 100 parts of water, 0'4- 



