RESPIRATION OF PLANTS. 
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in the endosperm, dissolving and chemically changing them, points to the way in 
which the absorption of food-material is effected by saprophytes which possess no 
chlorophyll, their absorbing organs probably first causing the solution and chemical 
transformation of the decaying organic constituents of the humus. The decaying 
foliage in which Monotropa, Epipogium \ and Corallorhiza grow, does not give up 
to water the serviceable materials which are still present in it, any more than the 
cellulose of the endosperm of the Date, or the starch of the endosperm of Grasses, 
or the oil of the seed of Ricinus, can be extracted by water ; but these saprophytes 
nevertheless obtain their nutriment from them. The fact that the roots of plants of 
this kind are so few in number and so diminutive in length, as in Neottia, or are 
entirely wanting, as in Epipogium and Corallorhiza^ is very remarkable in connection 
with this. These plants are concealed in the nutrient substratum till the time of 
flowering, and may act upon it by their whole surface ; and it is important to note 
that the absorbing surface of seedlings is very small in proportion to the great 
amount of work done, as is also the case with the absorbing roots of Cuscuta^ 
Orobanche, Sec. 
Sect. 6. — The Respiration of Plants ^ consists, as in animals, in the 
continual absorption of atmospheric oxygen into the tissues, where it Causes 
oxidation of the assimilated substances and other chemical changes resulting from 
this. The formation and exhalation of carbon dioxide — the carbon resulting 
from the decomposition of organic compounds — may always be directly observed ; 
the production of water at the expense of the organic substance in consequence 
of the process of respiration is inferred from a comparison of the analysis of 
germinating seeds with the composition of those which have not yet germinated. 
Experiments on vegetation show that growth and the metastasis in the tissues 
necessarily connected with it only take place so long as oxygen can penetrate 
from without into the plant. In an atmosphere devoid of oxygen no growth 
takes place ; and if the plant remains for any time in such an atmosphere it 
finally perishes. The more energetic the growth and the chemical changes in 
the tissues, the larger is the quantity of oxygen absorbed and of carbon dioxide 
exhaled ; hence it is especially in quickly germinating seeds and in unfolding 
leaf- and flower-buds that energetic respiration has been observed; such organs 
•consume in a short time many times their own volume of oxygen in the pro- 
duction of carbon dioxide. But in all the other organs also — in every indi- 
vidual cell — respiration is constantly going on ; and it is not merely the chemical 
changes connected with growth that are dependent on the presence of free 
oxygen in the tissues; the movements of the protoplasm also cease if the sur- 
rounding air is deprived of this gas ; and the power of motion possessed by 
periodically motile and irritable organs is lost if oxygen is withheld from them; 
^ See Reinke, Flora, 1873, No. 10-14. 
^ The special references for what is said on this subject will be found in my work on Expe- 
rimental Physiology, sect, 9, On the action of atmospheric oxygen. Of more recent works may 
be mentioned especially, Borscow, On the behaviour of plants in nitrogen (Melanges biologiques 
tires du Bulletin de I'Acad. Imp. des Sei. Nat. de St. Petersbourg, vol. VI, 1867); also Wiesner, 
Sitzungsber. der Wiener Akad. vol. LXVIII, 1871 ; Bert, Comptes Rendus, 16 Juin, 1873. [See also 
Wortmann, Arb. d. bot. Inst, in Würzburg, Bk. II, 1880; Pfeffer, Das Wesen und die Bedeutung der 
Athmung in der Pflanze, Landwirth. Jahrb. VII, 1878.] 
3 A 
