242 



BOTANY 



PART I 



a grain of Indian Corn, a full half of tlie organic reserve material is 

 consumed in three Aveeks. That green plants growing in the light 

 accumulate a considerable surplus of organic substance is due to the 

 fact that the daily production of material by the assimilatory activity 

 of the green portions is greater than the constant loss which is caused 



by the respiration of all the 



organs, 



Thus, according to 

 Boussingault's estimates, in 

 the course of one hour's assimila- 

 tion a plant of Sweet Bay will 

 produce material sufficient to 

 cover thirty hours' respira- 

 tion ('**). Plants produce in 

 twenty-four hours about five to 

 ten times their own volimie of 

 carbonic acid. In shade-plants 

 this is usually reduced to twice 

 the plant's volume, Avhile the 

 commonly cultivated Aqiidisim 

 produces only one -half of its 

 own volume, and can therefore 

 succeed even under conditions 

 which are unfavourable to as- 

 similation. 



In order to demonstrate the 

 existence of respiration either 

 the absorption of oxygen or the 

 giving oft' of carbon dioxide by 

 the plant may be employed. 

 If a handful of soaked seeds is 

 placed at the bottom of a glass 

 cylinder, the top of which is 



Fig. 204.— Experiment to demonstrate respiration, closed for a day by a glass plate, 



Tlie inverted flask (B) is partially filled with the OXygCU in the SpaCe is USed 



flowers which are lield in place by the plug of , ' P . . •■ 



cotton (W). Owing to the absorption of the ^^P '^7 ^"^ germuiating SCeclS ; a 



carbon dioxide exhaled in respiration by the caudlc will be extinguished if it 



solution of caustic potasii (K), the mercury (Q) jg introduced iuto the Cylinder. 



rises in the neck of the flask. . . - 



If germuiating seeds or flower- 

 heads of Compositae (B, Fig. 204) or young mushrooms are placed 

 in a flask and prevented from falling out when the flask is inverted 

 by means of a plug of cotton-wool (W), the mouth of the flask can be 

 dipped under mercury (S) ami some solution of caustic potash (K) be 

 introduced above this. The carbon dioxide formed is then absorbed 

 by the caustic potash and the mercury rises (Fig. 204). When this 

 experiment is carried out quantitatively it is found that a fifth of the 

 volume of air disappears, so that all the oxygen has been absorbed. 



F' 



