GASES. 



GASES. 



acid gas ; but the common oak (Quercus rofo/r), 

 the yellow stone crop (Sedutn reflexwn), and the 

 great majority of plants, emit a considerable 

 portion, not equal, however, in amount to the 

 oxygen gas which has been imbibed; and this 

 absorbed oxygen enters, there is little doubt, 

 into immediate combination with other sub- 

 stances, and forms vegetable matters in other 

 shapes. A variety of experiments have, in 

 fact, been made to ascertain this. Thus, th- 

 leaves of plants which have but recently ab- 

 sorbed a portion of oxygen gas have been ex- 

 posed in the exhausted receiver of an air-pump. 

 Other leaves have been submitted to the great- 

 est heat they could bear without undergoing 

 combustion, hut in neither case was any oxy- 

 gen gas extricated from them. And it has 

 been noted that those plants which absorb the 

 greatest proportion of oxygen during the night 

 are precisely those which evolve the most con- 

 siderable quantity of carbonic acid gas during 

 the day. 



Plants of different kinds vary very much in 

 the quantity of oxygen which they absorb. 

 Fleshy-leaved plants, which emit little or no 

 carbonic acid gas, absorb very little oxv_ r en ; 

 and these plants, it may be remarked (says 

 Dr. Thomson), can vegetate in elevated situa- 

 tions, where the air is very rarefied. Next in 

 order come the evergreen trees, which, al- 

 though they absorb more oxygen than the 

 fleshy-leaved plants, yet require much le^s than 

 those which lose their leaves during winter. 

 Those plants which flourish in marshy ground 

 likewise absorb but little oxygen. M. Saussure 

 tried a great number of experiments on this 

 subject, with a variety of plants of different 

 kinds. The following are some of his results : 

 in every case the weight of the leaves is sup- 

 posed to be equal to 1-00, and the bulk of oxy- 

 gen is expressed in the table. (Recherches, p. 

 99.) 



Quantity of Dry <eo 



Leaves of Evergreens. atxorbed. 



Primus laum-cerasus ... May 3'20 

 Vinca min<>r (li-ssrr periwinkle) - June 1-50 

 I'iinis ahies <tlu- tir) - - - -Sept. 3'00 

 Juniperus Sahma .... June 2 60 



Leaves of Trees vhich lots them in Winter. 



Quercus robur (the nak) - May 5-50 



Populus alba (the abele) - - - May 6-20 



----- Sept. 4 36 



Amygdalns Persica - ... June 6-60 



----- Sept. 4 20 



Rosa centifolia - - - - -June 5-40 



Leaves of Herbaceous Plants. 



Solanum tuberosum (the potato) - Sept. 2-50 



Brassica oleracea ((he cabbage) ) a 9-An 



young leaves 3 " 



old leaves - - Sept. 2-00 



Vicia faba (vetch), before flowering - 3-70 



in flower - 2 00 



after flowering - 160 

 Brassica rapa (the turnip), in flower 1-25 

 Avena saliva (the oat) ... June 2-70 

 Triticum aestivum .... May 5'00 

 Pisum sativmn (the pea) ... May 3 - 72 

 Ruta graveolens .... Aug. 2-00 



Sanssure continued his researches upon the 

 uses of oxygen gas^o vegetation. He found 

 that it was essential to many of its functions, 

 that it was absorbed not only by the leaves, but 

 by the^-oots of plants, that it then combined 

 with carbon, and the carbonic acid gas thus 

 formed was thence transmitted to the leaves to 

 be decomposed : the very stems and branches 

 of plants absorb it, and its presence is essen- 

 tial to the expansion of flowers ; in its absence, 

 seeds will not germinate, and hence the reason 

 why they will not vegetate when placed beyond 

 a certain depth in the soil. The quantity of 

 oxygen gas consumed during their germina- 

 tion, by equal weights of different seeds, varies 

 considerably. Wheat and barley consume 

 less oxygen than pease, and pease less than 

 common broad and kidney-beans the latter 

 consuming y^th part of their weight, while 

 wheat and barley,during their germination, only 

 absorb from T 7rirT th to 2ivW tn tneir weight of 

 oxygen gas. Recent experiments have shown 

 also, that the more water is impregnated with 

 oxygen gas, the more excellent are : u effects 

 uht-M employed for the purpose ol vatering 

 plants ; and hence one of the causes o the su- 

 periority of rain-water, every 100 cubic inches 

 of which contain 3-5 of oxygen LMS. Some 

 recent experiments were made by Mr. Hill, 

 which clearly demonstrated these facts. Hva- 

 cinths, melons, Indian corn, and other plants, 

 were watered for some time with water ini- 

 P reflated with oxygen gas; the first grew with 

 additional beauty and luxuriance, the melons 

 were improved in flavour, the Indian corn 

 increased in bulk, so as " to equal in size most 

 of those imported from North America," and 

 all of them grew more vigorously. 



The uses, therefore, of oxygen gas to plants 

 are many and important, and accord with the 

 conclusions which naturally suggest them- 

 selves from the results of the analysis of vege- 

 table substances, from whence oxygen is never 

 absent; it must be, therefore, one of the neces- 

 sary supporters of vegetable life. 



Nitrogen. This is the last atmospheric gas 

 which exerts its influence upon vegetation, and 

 enters in small proportions into the composi- 

 tion of plants. Entering in the large propor- 

 tion of 79 per cent, into the composition of 

 the atmosphere, it is yet supposed to exert but 

 a slight influence upon vegetation. It is found in 

 much smaller proportions in plants than either 

 oxygen gas or carbonic acid gas, although re- 

 cent researches have shown that it is much 

 more commonly present in vegetable sub- 

 stances than was once supposed; and as I 

 have elsewhere observed (Johnson on Fertilizers, 

 p. 338), that it exerts a more sensible influence 

 upon their growth than is commonly believed, 

 is very certain, and that the proportion of it 

 present in them varies with the different states 

 of their growth, has been clearly shown by the 

 experiments of Mr. Robert Rigg, who found in 

 100 parts of 



Part* of nitroeeifc 



The flour of wheat unripe - 2-9 



The same nearly ripe - - - 

 Leaves of wheat unripe 



nearly ripe 

 Stem of wheat unripe - 



nearly ripe 

 Chaff of wheat unripe - 



52? 



2-3 

 3-3 

 2-1 

 3-5 

 1-3 



