Dr. Gardner's Researches on the Functions of Plants. 431 



p. 407). It is evident the normal atmosphere of these fungi 

 contained an excess of nitrogen and carbonic acid. Th. 

 de Saussure found that seeds germinating in air absorbed 

 nitrogen, but when placed in a mixture of N 50, O 50, they 

 no longer did so {Mem. de la Soc. de Geneve, t. vi. p. 545). 



24. By overlooking the laws of penetration, DeCandolle, 

 Saussure, Ingenhousz, and Plenk are thrown into contradic- 

 tory positions in their experiments on the action of the green 

 parts of plants on artificial atmospheres. Thus DeCandolle 

 (Phys. Veg. t. i. p. 133), "Les parties verts laissent moins de 

 gas oxigene dans le gas bydrogene que dans le gas azote; 

 elles ne paraissent, contre 1'assertion d'Ingenhousz, absorber 

 ni l'un ni l'autre. II parait aussi certain, malgre l'assertion 

 de Plenk, qu'elles n'exhalent point de gas azote, sauf dans 

 quelques cas, par les corolles." 



25. In the summer of 1844 I tested this question by placing 

 some specimens of the Conferva mucosa in pump-water and in 

 carbonated water, and allowing them to act for several days 

 on the same water, l'emoving each day the gas generated du- 

 ring light; the plants were therefore subjected in their natural 

 medium to different mixtures of gases dissolved in the fluid. 

 The result was, that the plants in pump-water gave in six 

 hours a gas consisting of O 73, N 27 per cent. ; in twenty- 

 four hours, O 53, N 47 per cent.; in forty-eight hours, 

 O 18 '6, N 81*4 per cent. In carbonated water, in six hours, 

 O 68 per cent. ; in twenty-four hours, O 63 per cent. ; in 

 forty-eight hours, O 12, N 88 per cent.; in seventy-two 

 hours, O 3*5, N 96*5 per cent. And these plants continued 

 healthy and acted as before when fresh water was added. 



26. Conclusion. — From the preceding evidence I infer that 

 plants constitute a simple porous system. The advantages 

 resulting from this philosophical view of vegetation, both in 

 assimilating facts hitherto insulated and in criticising experi- 

 mental arrangements in vegetable physiology, constitute its 

 chief recommendation. For illustration, we adduce two ge- 

 neral laws springing from this theory: — 1st. No hypothesis 

 nor argument can be based on the composition of the gases 

 expired by plants without the strictest regard to the disturb- 

 ing influence of light, the gases of the soil-fluid. 2ndly. No 

 experiments on the action of plants in sun-light can be ac- 

 cepted in determining the functions of leaves unless made in 

 atmospheric air. 



27. Finally, I beg to present the following summary of 

 conclusions as fairly deducible from the preceding experi- 

 ments: — 



