148 OUTLINES OF PLANT LIFE. 



certain plants are capable of utilizing radiant energy of the 

 sun for food making, all must set free within their own 

 bodies the energy requisite for putting in place particles of 

 new material to form new parts, and for the execution of 

 movements, whether internal, such as the streaming or rota- 

 tion of the protoplasm, or mass movements, such as those of 

 leaves and other members, or movements of locomotion, such 

 as those of swarm spores and sperm cells. (See ^236 ff.) 

 The required energy is set free by the destruction of the sub- 

 stance formed when oxygen united with the protoplasm. 



EXERCISE XXXV. 



To show the necessity of respiration for growth. 



Germinate a number of beans in sawdust. Select eight with straight 

 roots about 2 cm. long. Clean and dry the surface slightly by brushing 

 with frayed edges of strips of filter paper, taking care not to expose roots 

 so long that they are injured by dry air. With a very fine sablehair brush 

 and thick Chinese (or waterproof black drawing) ink, mark each root by 

 distinct lines into ten spaces I mm. apart, commencing with tip. This 

 can be done most conveniently by pinning the seedling to a strip of soft 

 wood and laying alongside the root a ruler whose graduated edge has 

 been blunted by a plane until it is about 2 mm. thick. 



Pin half the seedlings to a strip of soft wood set into a jar partly filled 

 with wet sawdust, so that the roots will be vertical in damp air. Put 

 the other half into a, similar jar and cover them with water recently 

 boiled and cooled. After 24 hours, remeasure and compare total growth. 

 (See also Exercise XXXVI.) 



206. Loss of weight. — As a consequence there ensues a 

 loss of weight. If a plant, such as a seedling abundantly 

 supplied with reserve food, be compelled to develop in dark- 

 ness, and so allowed to make no additional food, it may be 

 easily demonstrated that a large part, often as much as one 

 half, of its weight will be lost (as gases) in respiration. This 

 loss of weight comes primarily from the decomposition of 

 portions of the living protoplasm. These, however, are soon 



