Page:Popular Science Monthly Volume 18.djvu/517

Rh A stick cut in the shape of Fig. 3 was purposely split at the short end, the split reaching beyond the hole. As the wood was highly

 (reduced to one half natural size), with a hole through which the radicle of a bean grew. Thickness of stick at narrow end, ·08 inch; at broad end, ·16. Depth of hole, ·1 inch.

elastic, the split closed as soon as it was made. The stick and bean were buried in damp sand, the bean being placed so that the radicle in growing would enter this hole. After six days they were dug up, and the radicle was found much enlarged above and beneath the hole. The fissure was open to a width of four millimetres, but as soon as the radicle was removed it closed to two m.m. The stick was then suspended horizontally by a fine wire passing through the hole, and a little saucer was suspended beneath it to receive the weights, and it required eight pounds eight ounces to open the fissure to the width of four m.m.

Again, "holes were bored near the narrow end of two wooden clips or pincers (Fig. 4), kept closed by brass spiral springs. Two radicles in damp sand were allowed to grow through these holes. The pincers rested on glass plates, to lessen the friction from the sand. The holes were a little larger and considerably deeper than in the trials with the sticks, so that a greater length of a rather thicker radicle exerted a transverse strain. After thirteen days they were taken up. The distance of two dots (see Fig. 4) on the longer ends of the pincers was now carefully measured; the radicles were then extracted from the holes, and the pincers of course closed. They were then suspended in the same way as the stick, and a weight of three pounds four ounces was necessary with one of the pincers to open them as much as the radicle had done by transverse growth." This radicle had escaped beyond the hole, and flattened a little, as soon as it had slightly opened the pincers, which had somewhat lessened the strain. As a result of all his observations, he concludes: The radicle "increases in length with a force equal to the pressure of at least a quarter of a pound, and much greater when prevented from bending"; and "it increases in thickness pushing away the damp earth on all sides with a force of eight pounds in one case and three pounds in another."