RESPIRATION OF PLANTS. "JQ,! 



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 

 transformatron 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 Ria'nus, 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 Neottta, 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, &c. 



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 Sci. 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 Wiirzburg, Bk. II, 1880; Pfeffer, Das Wesen und die Bedeutung der 

 Athmung in der Pflanze, Landwirth. Jahrb. VII, 1878.] 



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