CHAPTER \^. 



MECHANICAL USES OF WATER. 



111. Turgidity of plant parts. — As we have seen by the 

 experiments on the leaves, turgescence of the cells is one of the 

 conditions whicli enables the leaves to stand out from the stem, 

 and the lamina of the leaves to remain in an expanded position, 

 so that thev are better exposed to the light, and to the currents 

 of air. Were it not for this turgidity the leaves would hang 

 down close against the stem. 



112. Restoration of turgidity in shoots. — If we cut off a 

 living stem of geranium, coleus, tomato, or " balsam," and allow 

 the leaves to partly wilt so that the shoot loses its turgidity, it is 

 possible for this shoot to regain turgidity. The end ma}- be 

 freshly cut again, placed in a vessel of water, covered with a bell 

 jar and kept in a room where the temijerature 

 is suitable for the growth of the plant. The 

 shoot will usually become turgid again from 

 the water which is absorbed through the cut 

 end of the stem and is carried into the leaves 

 where the individual cells become turgid, and 

 the leaves are again expanded. Such shoots, 

 and the excised leaves also, may often be made 

 turgid again by simply immersing them in 

 water, as one of the experiments with the salt 

 solution would teach. 



FiR. 6i. 



Re.=;toration of turgidity 



(.Saclis). 



Tlierul .■II. 1 .,f tl 



sll, 



113. TiirgidiUMiiay be restored more ccrtainlv and 

 (|uickly in a |.aiiiall\' wilie.l sli.x.i in an. .liter wa\-. 

 it in;t\' l.e inserl.il iti a I" liil.e as sit, ,« n in fm. (,i_ i]-,^. 



enij t)i the Itiljc ar.jum! lite stem of tlie plant lieing itiadc air-lighl. The arr 



S6 



