20 



CIRCUMNUTATION OF SEEDLINGS. CHAP. I. 



Fig. 10. 



up and down, as Fig. 10 here stands) being a little lengthened 

 or shortened ; whereas any -lateral movement would be well 

 exhibited. The present tracing shows 

 that the cotyledon did thus move laterally 

 (that is, from side to side in the tracing) 

 12 times in the 14 h. 15 m. of observa- 

 tion. Therefore the cotyledons certainly 

 circumnutated, though the chief move- 

 ment was up and down in a vertical 

 plane. 



Rate of movement. The movements of 

 the hypocotyls and cotyledons of seedling 

 cabbages of different ages have now been 

 sufficiently illustrated. With respect to 

 the rate, seedlings were placed under the 

 microscope with the stage removed, and 

 with a micrometer eye-piece so adjusted 

 that each division equalled 5^ inch ; the 

 plants were illuminated by light passing 

 through a solution of bichromate of potas- 

 sium so as to eliminate heliotropism. 

 Under these circumstances it was interest- 

 ing to observe how rapidly the circum- 

 nutating apex of a cotyledon passed across 

 the divisions of the micrometer. Whilst 

 travelling in any direction the apex generally oscillated back- 

 wards and forwards to the extent of -^-^ and sometimes of nearly 

 2^0 of an inch. These oscillations were quite different from the 

 trembling caused by any disturbance in the same room or by 

 the shutting of a distant door. The first seedling observed was 

 nearly two inches in height and had been etiolated by having 

 been grown in darkness. The tip of the cotyledon passed across 

 10 divisions of the micrometer, that is, -^ of an inch, in 6 m. 

 40 s. Short glass filaments were then fixed vertically to the 

 hypocotyls of several seedlings so as to project a little above the 

 cotyledons, thus exaggerating the rate of movement ; but only a 

 few of the observations thus made are worth giving. The most 

 remarkable fact was the oscillatory movement above described, 

 and the difference of rate at which the point crossed the divi- 

 sions of the micrometer, after short intervals of time. For 

 instance, a tall not-etiolated seedling had been kept for 14 h. 

 in darkness ; it was exposed before a north-east window for only 



Brassica ole.racca : cir- 

 cunmutation of a 

 cotyledon, the hypo- 

 cotyl having been 

 secured to a stick, 

 traced on a horizon- 

 tal glass, in dark- 

 ness, from 8.15 A.M. 

 to 10.30 P.M. Move- 

 ment of the bead of 

 the filament magni- 

 fied 13 times. 



