Page:Popular Science Monthly Volume 18.djvu/515

Rh "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, 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 circumnutating 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 little 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 ∙11 inch. Had the filament been attached at first close to