120 GROWTH AND WORK OF PLANTS 



the leaves is also diffused to many other parts of the plant, the 

 growing buds, and also parts of the stem. Some succulent stems 

 are provided with stomates also, and the stems of shrubs and 

 trees are provided with openings called lenticels (paragraph 115) 

 through which there is an exchange of gases. 



192. Conditions of respiration. Light does not exercise 

 any important influence on respiration, but warmth is of fun- 

 damental significance. The minimum temperature at which 

 respiration takes place is a little below the freezing point (o 

 . = 32 F.) in most plants but it has been shown to be as low 

 as 10 C. As temperature increases the intensity of res- 

 piration increases up to a maximum intensity, which in most 

 plants is injurious to the other life processes, and then the in- 

 tensity decreases. The optimum temperature for respiration is 

 below the maximum, and is the highest temperature at which 

 the other life processes are not injured. This varies for differ- 

 ent plants. Water has no specific influence, but affects the 

 intensity of respiration through its effect on the other life pro- 

 cesses. Respiration ceases in completely dry plants (seeds, 

 dry mosses, dry lichens, certain spores) and is low or alto- 

 gether ceases in resting plants or parts of plants as in the autumn 

 and winter. Oxygen is necessary for ordinary respiration.* 

 But an increase or decrease in oxygen content of the air has little 

 immediate significance. 



193. Respiration in fungi. While fungi cannot form sugar, 

 or starch, they breathe like other plants. This can be shown by 

 placing a few half -grown mushrooms or toadstools in a fruit jar, 

 and closing it tightly. In 10 to 12 hours the test with the 

 barium hydrate and afterwards with the lighted splinter shows 

 the presence of carbon dioxide. 



194. Respiration necessary for growth. This can be 

 shown by the following experiment. Germinate some peas 

 until the radicles are 2 to 3 cm. (about i inch) long. Have ready 

 a bottle with soaked peas as described in- paragraph 186 and 

 with a small quantity of water in the bottom to keep the air in 



* Aerobic respiration, see foot-note, page 122. 



