306 THE FOOD OF PLANTS 



been induced in the plants employed by Bonnier that he was able to detect no 

 evolution of oxygen from them *. Other green parasites, such as the mistletoe 2 , 

 actively decompose carbon dioxide, and even Neottia nidus avis, when exposed to 

 bright light, gives off slightly more oxygen than it consumes, although it contains 

 only very little chlorophyll 3 . A distinct power of photosynthetic assimilation is 

 exhibited by the brownish and yellowish chloroplastids of Cuscuta cephalanti and 

 C. europaea (Ewart, I.e., p. 448), and the active photosynthesis of which red and 

 brown algae are capable has long been known 4 . All the lower animals which 

 contain definite chloroplastids can assimilate carbon dioxide when exposed to 

 light, and hence it is unnecessary to discuss whether these are symbiotic algae or 

 an actual part of the animal itself 5 . 



The photosynthetic assimilation of carbon dioxide is possible only 

 in the presence of chlorophyll or of etiolin, and hence non-green plants 

 or parts of plants exhale approximately the same amount of carbon 

 dioxide in the light as in darkness, as was first shown by Senebier and 

 de Saussure (Sect. 104). This applies not only to fungi and to roots, 

 but also to leaves which have become colourless and chlorotic owing to 

 a deficiency of iron G . 



It is easy to show by means of the bacterium-method that in each 

 single cell or mass of cytoplasm the power of evolving oxygen in the light 

 is directly dependent upon the presence of chlorophyll. On the other 

 hand, the chloroplastids can form starch in the darkness if supplied with 

 sugar, and this leucoplastic function may be exercised in the entire absence 

 of all chlorophyll (Sect. 55). 



The actual assimilation of carbon dioxide probably takes place entirely 

 in the chloroplastid, for by means of the delicate bacterium-method it 

 may be shown that isolated chloroplastids occasionally continue to evolve 

 oxygen in the light for a few hours, if placed in an isosmotic sugar 

 solution 7 . An isolated chlorophyll body may therefore, like a separated 



1 Bonnier, Compt. rend., 1891, T. cxm, p. 1074. Cf. Ewart, I.e., p. 446. 



2 Luck, Ann. d. Chem. u. Pharrn., 1851, Bd. LXXVIII, p. 85. 



3 Drude, Biol. v. Monotropa u. Neottia, 1873, p. 18. Cf. Wiesner, Flora, 1874, p. 73. 



1 Poiret, de Candolle, Physiol. d. Plantes, T. II, p. 703; Daubeny, Phil. Tmns., 1836, Pt. i, 



P- '53- 



'' [Both may be possible ; thus the yellow cells of Radiolaria and the chloroplastids of Hydra 

 viridis (Zoochloranthellae, Beyerinck) seem to be symbiotic algae (Brandt, Monatsber. d. Berl. Akad., 

 1 88 1, p. 388), whereas in Vorticella campanula the chlorophyll is diffuse, and forms part of the 

 animal's substance, and in the brown flagellate infusorian known as Peridinium (Ceratiuui) tripos 

 the diffuse assimilatory pigment seems likewise to form part of the body of the animal.] Cf. also 

 Biitschli, Protozoen, 1887-9, Bd. ill, p. 1473; Dantec, Ann. d. 1'Inst. Pasteur, 1892, T. vi, p. 190, 

 and the literature here quoted. See also Sect. 65. 



6 Pfeffer, Physiol., i. Aufl., Bd. I, p. 185 ; Zimmermann, Beitrage z. Morph. u. Physiol., 

 J893, P- 30- 



7 Engelmann, Bot. Zeitung, iSSi, p. 446; Haberlandt, Function u. Lage d. Zellkernes, 1887, 

 p. 118; Ewart, Journ. of Linn. Soc., 1896, Vol. xxxr, p. 423. Observations made upon the chloro- 



