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. another method of
observation, when much magnification of the movement was not required, will
presently be described. 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. The figures thus traced were therefore angular;
but if dots had been made every 1 or 2 minutes, the lines would have been
more curvilinear, as occurred when radicles were allowed to trace their own
courses on smoked glass-plates.
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