12 Curtis: Turgidity in Mycelia 



be considered as the response of the irritability of the protoplasm 

 due to shock. In fact, the measurements obtained by Townsend 

 by injuring the hyphae and observing the period of recovery cor- 

 respond with some of the above measurements. This shock also 

 entered as a factor in the changes from low to higher concentra- 

 tions, but the periods of recovery constantly grew longer in as 

 much as the accumulation of turgor force is a slow process and 

 requires more time than recovery from shock. In the cases where 

 we are dealing with a reduction of the turgor force a comparative 

 short period, i. e., the recovery from shock, is sufficient to adjust 

 the turgor since this is brought about by purely physical laws. 

 The accumulation of high pressures in the plants retarded in their 

 growth by NaCl and the low turgor of the plants growing rapidly 

 in solutions of slightly lower concentration, a phenomenon that has 

 often been discussed, seem to point to the same conclusion. A 

 certain maximum turgor force is necessary to start growth. If 

 for any reason growth is checked there follows an increase of the 

 pressure tending to continue the normal growth. Under the re- 

 verse conditions a rapid growth lowers the pressure which is, how- 

 ever, high enough to play its role in growth. Eschenhagen has 

 demonstrated that the turgor pressure of fungi is considerably in 

 excess of the substratum in which they are growing and this is to 

 be looked upon as an adaptive provision permitting changes of 

 substratum. It is possible that there must also be a certain excess 

 of turgor to inaugurate growth and higher than is actually required 

 to sustain it. Naturally a rapid growth expends a portion of this 

 surplus reducing turgor. These variations of pressure are com- 

 parable to the work done in overcoming the inertia of an object at 

 rest, a greater force is required to start the motion that is neces- 

 sary to maintain it. A better comparison is found in a water reser- 

 voir with a constant supply and a siphon discharge. A certain 

 maximum volume of water is required to bring the siphon into 

 action, but once in action it will continue the flow of water, though 

 the volume in the reservoir is greatly reduced. Furthermore, by 

 reducing the caliber of the siphon the volume rises, but by increas- 

 ing it the volume diminishes in both cases in proportion to the 

 area of the siphon. 



Turgor then is regulatory in its action. We can neither say 



