xxvi.] BOTANY. 105 



159. Transpiration. Cut two branches of the 

 same plant. Put one in a warm, the other in a cool 

 place. Note that the former fades soonest. With a 

 sufficiently delicate pair of scales this may be shown to 

 arise from a larger loss of water. Evaporation proceeds 

 more rapidly in warm air than in cold, because the 

 former is able to hold a larger amount of moisture. 



160. Germination. Suspend an acorn or horse- 

 chestnut by a piece of twine in the neck of a wide- 

 mouthed bottle, and above the surface of some water. 

 Place the bottle in a warm place. The water will 

 evaporate and moisten the suspended seed, which will 

 germinate. The condensed water is necessarily pure, 

 and it is evident that this is the only material required 

 by seeds in order to germinate. 



Repeat the experiment with two sets of bottles ; 

 place some in a warm, others in a cooler place. 

 Compare the time in which germination is effected. 



161. Effect of light on chlorophyll. Sow 

 some cress seed, and keep the pots in a dark place. 

 The seed-leaves will be pale. Remove part of the 

 germinating plants to the light ; the seed-leaves will 

 become green. Compare their progress in this respect 

 with those kept in the dark. 



Press closely upon the surface of a geranium leaf 

 some pieces of tin-foil, and afterwards expose the leaf 

 for five to ten minutes to bright sunlight. The parts 

 covered with the tin-foil will be found to have a darker 

 colour than the rest. The lighter tint is due to the 

 movement of the chlorophyll granules under the in- 

 fluence of light from the upper and lower surfaces of 

 the cells to their sides. 



162. Colour of flowers independent of light. 



