IV 



Movement and Nervous Action in Plants 73 



path of the young stem of a seedhng cabbage during 

 ten hours. How did Darwin get this record ? 



" Plants growing in pots were protected wholly from the 

 light, or had light admitted from above, or on one side, as 

 the case might require, 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 part to be observed by means of 

 shellac dissolved in alcohol. The solution was allowed to 

 evaporate, until it became so thick that it set hard in two 

 or three seconds, and " it never injured the tissues, even the 

 tips of tender radicles, to which it was applied." (?) 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 black 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 

 horizontal or vertical glass-plate (according to the position of 

 the object), and when one exactly covered the other, a dot was 

 made on the glass-plate with a sharply-pointed stick dipped in 

 thick Indian ink. Other dots were made at short intervals 

 of time, and these were afterwards joined by straight lines." 



Of course the result was not a picture, only a record of 

 the plant's path, showing nothing more than the general 

 character of the movement. 



Another method, which, however, is only in a few cases 

 practicable, is to allow the moving parts — radicles, for 

 instance — to trace their own paths, to write, as it were, 

 their own diary, on smoked plates of glass. Figures of 

 these root-tracks are given by Darwin in abundance, and 

 the student, in this case as the preceding, may profitably 

 endeavour to make them for himself 



