INFLUENCE OF EXTERNAL CONDITIONS ON GROWTH 



301 



ness. Thus, Bassler 1 showed that, in plants that bear no lateral branches, de- 

 capitation of the main stem produces, within twenty-four hours, an upward 

 bending of the leaves nearest the cut. The leaves may thus move through 

 arcs of from 5 to 30 degrees, and even more in some plants. The reaction is 

 more pronounced the nearer the leaves are to the wound. The wounding of 

 the stem by a longitudinal incision fails to produce the response of leaf move- 

 ment. Vochting observed a still more remarkable case than those just men- 

 tioned. The removal of the inflorescence from a plant of Brassica rapa var. 

 oleifera produced such a marked upward bending of the uppermost leaf that the 

 latter became quite vertical. 2 



Plants can withstand a very rapid rotation upon the centrifuge, so that aleu- 

 rone grains, starch grains and nuclei may be displaced in the cells; nucleoli may 



oOOOQ 0aoaaaaoaa aao ( 



Fig. 146. — Mycelium of Mucor racemosus, 

 grown in sugar solution (A), and in peptone solu- 

 tion (B). (After Klebs.) 



Fig. 147. — Diagrammatic representa- 

 tions of various forms of Bacillus sub- 

 tilis; for description see text, preceding 

 page. (After H . Buchner.) 



be thrown out of the nuclei and raphides may be made to penetrate through 

 the cell walls. 3 



§7. Influence of Nutrition on Growth and Configuration. — If ordinary green 

 plants are grown in mineral nutrient solutions, the nature and concentration 

 of the solution determine not only the rate of growth, but also the configuration 

 and the internal anatomy of the plant. This relation of developmental phe- 

 nomena to the conditions of nutrition is still more clearly evident in the case of 

 lower plant forms that are nourished by absorbed organic substances. Mucor 

 racemosus, for example, produces thick hyphae with blunt branches in sugar solu- 



1 Bassler, Friedrich, Ueber den Einfluss des Dekapitierens auf die Richtung der Blatter an orthotropen 

 Sprossen. Bot. Zeitg. 67 7 : 67-91. 1909. 



2 Vochting, Hermann, Untersuchungen zur experimentellen Anatomie und Pathologie des Pflanzen- 

 korpers. Tubingen, 1908. See Taf. 18, Fig. 2; Taf. 19, Fig. 9. 



3 Andrews, Frank Marion, Die Wirkung der Centrifugalkraft auf Pflanzen. Jahrb. wiss. Bot. 28: 1-40. 



