LIGHT AND LIFE. 105 



gen retained by the plant is replaced by nitrogen thrown 

 off; and supposed that this nitrogen was furnished by the 

 substance of the plant itself. This function of the green 

 portions of vegetables is, moreover, performed with great 

 rapidity and energy. Boussingault, who has made some 

 remarkable experiments on this subject, filled a vessel of 

 water with vine-leaves, placed it in the sun, and sent a cur- 

 rent of carbonic acid through it ; on its passing out, he col- 

 lected nothing but pure oxygen. It is calculated that a 

 leaf of nenuphar gives out in this way during the summer 

 more than sixty-six gallons of oxygen. 



In 1848 Cloez and Gratiolet contributed new facts. 

 They showed that aquatic plants follow the same course 

 during the day as others, but that at night they are at rest, 

 and give rise to no release of carbonic acid. They proved 

 the powerful, instantaneous action of solar light on vege- 

 table respiration. If a few leaves of potamogeton or of 

 nayas are put into a gauge full of water saturated with 

 carbonic acid, as soon as the apparatus is placed in the sun, 

 an immense number of light bubbles, of almost pure oxygen, 

 are seen to detach themselves from the surface of the leaves. 

 The shadow of a slight cloud, crossing the sky, suffices to 

 check their disengagement at once, followed by sudden 

 activity after it has passed. By intercepting the solar 

 beam with a screen, the alternations of quickness and slow- 

 ness in the production of gas-bubbles may be very plainly 

 seen, according as the plant receives the rays or not. Wa- 

 ter-plants show other interesting peculiarities. Diffused 

 light has no power to excite the production of carbonic 

 acid, unless the phenomenon has been first called forth by 

 direct sunlight. Still further, the solar influence having 

 once been applied, the evolution of carbonic acid continues 

 even in darkness. The vegetable keeps up at night its 

 mode of breathing by day. The living force of solar light, 

 therefore, can be fixed and stored away in living plants, as 



