DARWIN ON THE MOVEMENTS OF PLANTS. 499 



" Plants growing in pots were protected wholly from the light, or 

 had light admitted from above, or on one side, as the case might re- 

 quire, and were covered above by a large horizontal sheet of glass, and 

 with another vertical sheet on one side. A glass filament, not thicker 

 than a horse-hair, and from a quarter to three quarters of an inch in 

 length, was affixed to the j)art to be observed by means of shellac dis- 

 solved in alcohol, which was so thick as to set hard in two or three 

 seconds ; and it never injured the most delicate tissues. To the end 

 of the glass filament an excessively minute bead of black sealing-wax 

 was cemented, below or behind which a bit of card with a dot was 

 fixed to a stick driven into the ground. The weight of the filament 

 was so slight that even small leaves were not perceptibly pressed down. 

 The bead and the dot on the card were viewed through the glass plate, 

 and when one exactly covered the other a dot was made on the glass 

 plate with a sharply pointed stick dipped in Indian ink. Other dots 

 were made at short intervals, and they were afterward joined by 

 straight lines. The figures are therefore angular. If the dots had 

 been made every one or two minutes, the lines would have been more 

 curved, as when radicles traced their own courses on smoked-glass 

 plates. "When the dot on the card was half an inch from the bead of 

 sealing-wax, and the glass plate (supposing it to have been curved) 

 stood seven inches in front, the tracing represented the movement of 

 the bead magnified fifteen times." 



Another, and in some respects better, method was used when it was 

 required to magnify the movement. The dots on the glass plate were 

 copied upon tracing-paper, and joined by ruled lines with arrows to 

 show direction, the first dot being made larger to catch the eye. Night 

 movements are shown by broken lines. 



Chapter I is devoted to the circumnu- 

 tating movements of germinating plants 

 or seedlings. The first experiment relates 

 to the movements of the young rootlet or 

 radicle of a seedling cabbage. In this 

 case fuller details of the process are given, 

 along with the diagram, than in any other, 

 for which reason we reproduce it here. 



" A seed, with the radicle projecting 

 05 inch, was fastened with shellac to a lit- 

 tle plate of zinc, so that the radicle stood 

 up vertically; and a fine glass filament was 

 then fixed near its base, close to the seed- 

 coats. The seed was surrounded by bits 

 of wet sponge, and the movement of the 

 bead at the end of the filament was traced 

 (Fig. 1) during sixty hours. In this time the radicle increased in length 

 from '05 to 'll inch. Had the filament been attached at first close to 



Fig 



1. Brasstca Oleracea: circnm- 

 nutation of radicle, traced on hori- 

 zontal glass, from 9 A. m., January 

 3l8t. to 9 p. M., February 2d. Move- 

 ment of bead at end of filament mag- 

 nified about forty times. 



