MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 15 



conditions. These experiments did not clearly demonstrate the re- 

 tarding influences of light, however. This is also true of von Wol- 

 koff's measurements as described by Sachs. ^'' 



Koch's *^ examinations of etiolated stems of cereals revealed the 

 imperfect development of certain tissues of mechanical value which 

 resulted in the " laying " of plants when grown too closely crowded. 

 Decrease of illumination was found to cause an exaggerated extension 

 of stems due to the greater elongation of their components, and was 

 accompanied by an attainment of a diameter below the normal. Such 

 changes ensued only in organs treated while in the earlier stages of 

 growth and as these alterations rested upon the action of existing 

 cells rather than upon the formation of new elements, the elongation 

 was greatest in the basal portions of internodes. Less thickening 

 ensued in the walls of such elongated elements but lignification pro- 

 ceeded in the customary manner. 



In some investigations of the relation of light to the construction , 

 and disintegration of chlorophyl, Wiesner*^ found that this substance 

 might originate in an etiolated specimen in an illumination too faint 

 to be discerned by the eye, a fact of great importance in imperfect 

 etiolation. Disintegration ensued only when light of sufficient in- 

 tensity to cause food formation was allowed to act upon the plant. 

 The formation of chlorophyl in etiolated plants ensued most quickly 

 in rays passing through a solution of cupric ammonia. 



The self-nutrition theory of G. Kraus and others was affirmed 

 by C. Kraus in some publications in 1875,^" and he also concurred in 

 the theory of Sachs that light retards growth by its direct action. 

 Later C. Kraus attempted a refutation of the principal results of 

 Godlewsky's earlier researches. 



Walz^' performed a series of tests of wide inclusiveness in 1875 

 in which it was confirmed that spores of ferns and oospores of 



«' Sachs. Text Book of Botany, 2d Ed, p. S35. 



^^Koch. Abnorme Aenderungen wachsender Pflanzenorgane durch Beschattung. 

 Berlin 1872. 



■*" W iesner, J. Vorlaufige Mittheilung iiber den Einfluss des Lichtes auf Entste- 

 hung und Zerstdrung des Chlorophylls. Bot. Zeitung, 32 : 116. 1874. 



50 Kraus, C. Pflanzenphysiologischen Untersuchungen. VI. Wachstum und 

 Chlorophyllbildung. Flora, 58 : 346. 1S75. 



Kraus, C. Ursachen der Formanderung etiolirter Pflanzen. Bot. Zeitung, 37 : 

 332. 1879. 



5'Walz, J. W. Ueber die Wirkung des Lichtes auf einige Processe des Pflanzen- 

 lebens. Schrift. d. k. Neuruss. Univ. i. Odessa, 17 : —. 1S75. Abstract in Bot. Jahr- 

 esber. 3: 7S6. 1875. 



