GROWTH 



215 



and therefore the stem (or leaf), points. The adoption of 25 cm. (10 inches) 

 as a standard distance from filament to glass has the advantage of permit- 

 ting different records to be directly compared. 



Other Methods of Studying Circumnutation. The above method was 

 introduced by Darwin (described in his book, "The Power of Movement 

 in Plants"), and has not teen improved since his time. It has obvious 

 drawbacks, one of the most serious being the error introduced into the record 

 as the filament points out more and more obliquely to the plate. This 

 error can be largely overcoire by use of a curved glass with the filament 

 lying in the radius. Such glasses can be obtained, and when placed, for 

 ■example, upon the tops of flower-pots which have seedlings growing near 

 their bottoms, yield very satisfactory records; but they have the drawback 

 that these records cannot be transferred to a flat surface for preservation 

 or publication. Another method of preventing this error is that of Wiesner 

 (Bewegungsverrr.ogen der Pflanzen, 1881), who used a blackened tube, 

 with cross wires, resting upon a glass plate; this is slipped about until the 

 filament or tip is covered by the. cross of the wires, when the record mark 

 is made upon a second glass plate placed beneath the first. A modification 

 of his method, requiring only a single plate, has been described by Stone 

 in the Botanical Gazette, 22, 1896, 262. A q-'ile different method of record- 

 ing circumnutation was that of Dewevre and Eordage (Revue generale 

 de Botanique, 4, 1892, 65), who photographed at intervals the position of 

 the whitened tip of the filament, but the method is of very moderate value. 

 Still another distinct method is that of Fritzsche, described in a paper 

 which is the only important recent work upon the subject (Ueber die Eeein- 

 flussung der Circumnutation durch verschiedene Faktoren, Leipzig, Oswald 

 Schmidt, 1899). He used a microscope arranged to be moved by screws 

 above the parts studied, and followed the movements directly upon an ocular 

 micrometer ruled in squares, a record being made upon the corresponding 

 squares of a ruled paper. It is also possible to study the circumnutation 

 of roots. This can be done by growing thern upon inclined smoked-glass 

 plates, as Darwin did ("Power of Movement in Plants"). But it can also 

 be accomplished by more direct methods as follows. Prepare a cylindrical 

 glass moist-chamber like that shown in figure 59, and arrange a strong 

 young root to grow in its axis. Down the outside of the chamber, 90 of 

 the circumference apart, rule two fine black lines; then, facing these 

 lines and 25 cm. from the root, set up two glass plates, so that it will be pos- 

 sible to sight through them and record the position of the roots as brought 

 into coincidence with the black line beyond. Thus an accurate record of 

 the nutation is obtainable. Of course the chamber should be kept dark- 

 ened except while the actual record is being made. 



Materials. These, for the plants accessible to the American teacher, 

 have been studied fully in my laboratory by Miss Hope Sherman, who 

 has used both Darwin's original method and Fritzsche's microscope 

 method. She has confirmed the well-known fact that seedlings have a 

 more active movement than older plants, and that in general the more 

 slender a part is, the greater is its movement. Of plants readily available 



