240 M. Marcet on the Changes which the Atmosphere 



It will be perceived, that in this instance nearly the whole of 

 the oxygen, viz. 7.16 cubic feet out of 7.84, was absorbed du- 

 ring the time the mushrooms were under the receiver, and had 

 combined with the carbon of the plants, to form an equal vo- 

 lume of carbonic acid gas. Besides this, the mushrooms evolved 

 about 1.02 of carbonic acid from the whole plants. 



A comparative experiment, conducted in darkness for twelve 

 hours, gave a result very nearly approximating to the above, 

 but with this difference, that, the quantity of carbonic acid 

 formed, was somewhat more considerable during the night than 

 during the day. 



It is on purpose that, in these latter experiments, I have 

 made the examination of the Boletus versicolor to succeed that 

 of the Agaricus digitaliforrnis* The influence of these two 

 species on the atmosphere, appears almost conclusively to de- 

 monstrate, that the absorption of oxygen and the formation of 

 carbonic acid in the experiments which precede, did not arise, 

 at all events in any considerable degree, from the commence- 

 ment of decomposition. In fact, we find that in the case of 

 Agaricus digitalrformis (see 4th Experiment), mushrooms of a 

 soft consistence, and of such as were beginning to waste away, 

 there was much less oxygen absorbed, and much less carbonic 

 acid disengaged, than in the case of the Boletus versicolor, where 

 the mushrooms are extremely tough, and of whose thriving vi- 

 tality we can entertain no doubt, since they were removed along 

 with the fibrous bed in which they were nourished, and so placed 

 under the receiver. 



Many other mushrooms have been successively submitted to 

 experiment in the same manner as the preceding, but as the re- 

 sults did not differ from those already obtained, except as to the 

 proportions of the oxygen absorbed, and the carbonic acid dis- 

 engaged, I have thought ii unnecessary to supply the details. 



Sect. II. On the Action of Mushrooms upon pure Oxygen Gas. 



1st Experiment — Two mushrooms of the species Agaricus 

 amarus, together weighing 90 grains, were placed, as soon as 

 they were removed from the soil, under a receiver which con- 

 tained 27.18 cubic feet of pure oxygen gas, the thermometer 

 standing at 68° Fahr. There they remained in full day-light 



