94 BOTANY. 



and Indian corn in eacli of two flower-pots and place one of tlie pots 

 in a cool cellar and the other in a warm room. Note differences in 

 growth in the plants in each pot, and also compare growth of similar 

 plants in the two pots. 



(6) Observe the average daily temperature during the time that the 

 hickory-trees are opening their buds in the spring. Compare this 

 with the average temperature during the time of most vigorous de- 

 velopment of the leaves and twigs, and also during the time of the 

 development of the fruit. 



(c) With a thermometer measure the temperature of the water of 

 ponds and ditches when the earliest vegetation appears in the spring. 

 This consists for the most part of diatoms, which form a brownish 

 scum on the water or a brown coat on sticks and stones. 



(c2) Measure in like manner the temperature of cold springs in 

 which vegetation is found. 



(e) When Indian com is producing its flowers (tassels and silk), ob- 

 serve the average temperature of the air and compare it with the 

 temperature of the soil at the average depth of the roots. 



(/) Enclose a small plant of Coleus (a common ' ' foliage-plant ") 

 and a clover-plant in a tin pail, covering them loosely. Enclose also 

 a thermometer. Set the pail in a tub of ice-water, allowing it to 

 remain for an hour or two. Note the effect upon each plant. Or 

 make the experiment by first growing little plants of wheat and 

 pumpkin or squash, and using these. The wheat will survive ; the 

 pumpkin or squash will not. 



Now make an experiment substituting hot water, and using a 

 spring plant (as hepatica or anemone) and a summer plant (as Indian 

 corn). Raise the temperature to 40° Cent. (104° Fahr.) and then in 

 crease the heat very slowly beyond this point. Notice effect ujjon 

 each plant. 



(jg) In the autumn notice that some plants are killed by frosts which 

 leave others unharmed. 



(7i) Thaw out two frozen apples, one in warm water rapidly, and 

 the other in ice-water slowly. The first will be more injured, the 

 second less. 



168. Light. — Directly or indirectly all plants are de- 

 pendent upon the light. Although many parasites and 

 saprophytes grow in complete darkness, they do so by 

 using material which developed in the light. We have 

 seen (par. 136) that carbon-assimilation is possible in the 

 light only in cells containing chlorophyll. All the carbon of 



