240 BOTANY PART i 



by the respiration of all the organs. Thus, according to Boussix- 

 GAULT'S estimates, in the course of one hour's assimilation a plant 

 of Sweet Bay will produce material sufficient to cover thirty hours' 

 respiration. Plants produce in twenty-four hours about five to ten 

 times their own volume of carbonic acid. In shade-plants, according 

 to GRIFFON, this is usually reduced to twice the plant's volume, 

 while the commonly cultivated Aspidistra produces only one-half 

 its own volume, and can therefore succeed even under conditions 

 which are unfavourable to assimilation ( : " >T ). 



A means of judging of the importance of respiration is afforded by 

 the behaviour of the plants themselves when deprived of oxygen. By 

 placing them, for example, under a jar containing either pure nitrogen 

 or hydrogen, or in one from which the air has been exhausted, it will 

 be found that all vital activity soon comes to a standstill ; plants, 

 previously growing vigorously, cease their growth ; the streaming 

 motion of the protoplasm in the cells is suspended, as well as (with 

 few exceptions, e.g. Mimosa and Drosera) all external movement of the 

 organs. If oxygen be admitted, after not too long an interval, the 

 interrupted performance of the vital functions is again renewed. 

 A longer detention in an atmosphere devoid of oxygen will, however, 

 irrevocably destroy all traces of vitality ; as in every condition of 

 rigor internal chemical changes take place which, by a prolonged 

 exclusion of oxygen, lead to the destruction and disorganisation of 

 the living substance. THE PRESENCE OF OXYGEN is NECESSARY TO 



THE CHEMICAL PROCESSES TAKING PLACE WITHIN THE CELL, IN ORDEU 

 TO MAINTAIN THE LIVING SUBSTANCE IN A CONDITION OF NORMAL 

 ACTIVITY. 



The absorption of oxygen and the evolution of carbonic acid by living plants 

 can be demonstrated both qualitatively and quantitatively by simple experiments. 

 From what has already been said of the antagonistic nature of assimilation and 

 respiration, it will be at once apparent that these experiments must be conducted 

 either in the dark or on portions of plants devoid of chlorophyll. The more 

 abundant the protoplasm and the more energetic its vital activity, so much the 

 more vigorous is the respiration. The best results are obtained, therefore, from 

 young portions of plants in an active state of growth. It should also be mentioned 

 that in the following experiments only the carbonic acid and not the whole of 

 the products of the respiratory activity are determined. From theoretical con- 

 siderations, and also from exact chemical analysis, it has been definitely established 



that, IN ADDITION TO CARBONIC ACID, WATER IS FORMED FROM THE OllUANH' 

 MATTER BY RESPIRATION. 



The absorption of oxygen and the formation of carbonic acid may be clearly 

 shown by the following experiment (Fig. 211). A flask (J?) partly filled with young 

 mushrooms or flower heads of a Composite is inverted with its mouth in an open 

 vessel of mercury (Q), and a few centimetres of caustic potasli solution (AT) introduced 

 within its neck. In the same degree as the carbonic acid produced by respiration is 

 absorbed by the caustic potash, the volume of air in the flask will be reduced and 

 the mercury will rise in the neck. After a time, the ascent of the mercury ceases 

 and it remains stationary. If the quantity of air remaining in the flask be esti- 



