196 TRANSPIRATION 



(iii) Some plants have been found to transpire slightly at tem- 

 peratures below freezing-point. Increasing the temperature within 

 certain limits accelerates the opening of the stomata, and even 

 in parts of plants free from these openings transpiration is 

 augmented thereby. 



(iv) Plants exposed to draughts and stronger currents of air lose 

 considerable amounts of water even when the stomata are closed. 



(v) A great decrease of water within the soil in which a plant 

 is growing results in decreased transpiration. 



The absorption of a somewhat concentrated solution also 

 decreases transpiration; and plants which have taken up con- 

 siderable amounts of common salt transpire less than those 

 which have no access to this substance. 



Sachs and others found that the alkalies, potash, soda and 

 ammonia in small quantities tended to increase transpiration, 

 while acids decreased it. 



Ex. 111. — Collect water from a leaf of = sunflower or other plant in a test- 

 tube arranged as in Fig. 85. 



Ex. 112. — (a) Take three flasks, each holding about 100 or 150 c.c, and 

 pour water into each until about three-quarters fiill. 



Cut two similar branches 2 feet long from an apple tree and remove the 

 leaves from one of them ; place the branches in two of the separate flasks, 

 and after marking the level of the water in each flask with a piece of gummed 

 stamp paper, expose all three flasks in a well-lighted window or out of doors. 

 Observe the loss of water in each flask after six hours : which branch tran- 

 spires most ? 



{b) To obtain a more accurate knowledge of the loss of water, weigh each 

 of the flasks and the branches separately at the commencement and the end 

 of the experiment. It will be observed that the water taken up by the 

 leafy branch is not merely absorbed into its substance but is transpired 

 by its leaves, for its weight at the beginning and end of the experiment are 

 nearly the same, although the weight of water lost from the flask has been 

 considerable. 



(<-) Repeat the experiment, but keep the apparatus in a dark room. 



Ex. 113.— Transpiration from a shoot maybe demonstrated by arranging 

 as in Fig. 86. Push the freshly cut shoot {a) through a bored cork: it 

 should fit the hole in the cork tightly and should project a little way through 

 it. Fill the U-tube («) completely with water and put the cork and shoot 



