ASSIMILATION OF CARBON 



27 



the color of Oscillaria. This alga tends to assume the color complementary to 

 that of the light acting upon it, and the longer the organism remains in the 

 colored light the more pronounced is the response. The following kinds of 

 illumination produced the following colorations in the organism. 



Color of Light Color or Alga 



Red Green 



Brownish-yellow Blue-green 



Green Reddish 



Blue Brownish-yellow 



The principle illustrated by this phenomenon was designated by Gaidukov as 

 the law of complementary chromatic adaptation. 



The amount of light 1 necessary for the decomposition of carbon dioxide is 

 closely related to the individual properties of the plant, some forms needing 

 more and others less light. Trees were long ago differentiated by students of 

 forestry into two types, heliophobous (shade plants) and heliophilous (non-shade 

 plants); among the first are included, for example, Abies (fir), Taxus (yew), 

 Fagus (beech), Tilia (linden); among the latter, Pinus (pine), Larix (larch), 

 Betula (birch), Robina (locust). 



Fig. 16. — Schistostega osmundacea: A, protonema; B, diagram representing the path taken by 

 rays of light as they enter and leave the cells of the protonema. 



Schistostega osmundacea, a moss that grows in dark caves, may be mentioned 

 as an example of plants that can thrive in extremely weak light. Its protonema 

 has a very peculiar structure (Fig. 16), and, although existing in semi-darkness, 

 it appears emerald green. Single filaments of the protonema, as they grow 



1 Kreusler, U., Ueber eine Methode zur Beobachtung der Assimilation und Athmung der Pflanzen und 

 iiber einige diese Vorgange beeinflussende Momente. Landw. Jahrb. 14: 913-965. 1885. Timiriazeff, 

 C, Sur le rapport entre l'intensit6 des radiations solaires et la decomposition de l'acide carbonique par les 

 veg6taux. Compt. rend. Paris 109: 370-382. 1889. Pantanelli, Enrico, Abhangigkeit der Sauerstoff- 

 ausscheidung belichteter Pflanzen von aiisseren Bedingungen. Jahrb. wiss. Bot. 39: 167-228. 1904. 

 Lubimenko, W., Sur la sensibilite de l'appareil chlorophyllien des plantes ombrophiles et ombrophobes. 

 Rev. gen. Bot. 17: 381-415. 1915. Idem, concentration du pigment vert et l'assimilation chlorophyl- 

 lienne. Ibid. 20: 162-177, 217-238, 253-267, 285-297. 1908. Idem, Production de la substance seche 

 et de la chlorophylle chez les v6g6taux sup6rieurs aux differentes intensites lumineuses. Ann. sci. nat. 

 Bot. IX, 7: 321-415. 1908. 



