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Show 74 ACTION OF THE RADICLE. 0HA1'. Il radicle was then allowed to grow into a narrow hole in wood, 2 or 3 tenths of an inch in depth, and closed at .the bottom. The wood was so cut that the short space of radicle between the month of the hole and the bean could not bend laterally on three sides; but it was impossible to protect the fotuth side, close to ,the bean. Consequently, as long as the radicle continued to increase in length and remained straight, the weighted bean would be lifted up after the tip had reached the bottom of the shallow hole. Beans thus arranged, surrounded by damp sand, lifted up a quarter of a pound in 24 h. after the tip of the radicle had entered the hole. With a greater weight the radicles themselves always became bent on the one unguarded side; but this probably would not have occurred if they had been closely surrounded on all sides by compact earth. There was, however, a possible, but not probable, source of error in these trials, for it was not ascertained whether the beans themselves go on swelling for several days after they have germinated, and after having been treated in the manner in which ours had been; namely, being .. first left for 24 h. in water, then allowed to germinate in very damp air, afterwards placed over the hole and almost surrounded by damp sand in a closed box. Fig. 55. s Outline of piece of stick (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. We succeeded better in ascertaining the force exerted transverse! y by these radicles. Two were so placed as to penetrate small holes made in little sticks, one of which was cut into the shape here exactly copied (Fig. 55). The short end of the stick beyond the hole was purposely split, but not the opposit~ CJIAI'. II. ACTION OF THE RADICLE. end. As the wood was highly elastic, the split or fissure closed immediately after being made. After six days the stick and bean were dug out of the clamp sand, and the radicle was found to be much enlarged .above and beneath the hole. The fissure, which was at first quite closed, was now open to a width of 4 mm. ; as soon as the radicle was extracted, it immediately closed to a width of 2 mm. rrhe stick was then suspended horizontally by .a fine wire passing through the hole lately filled by the radicle, and a little saucer was suspended beneath to receive the weights; and it required 8lbs. 8 ozs. to open the fissure to the width of 4 mm.-that is, the width before the root was extracted. But the part of the radicle (only ·1 of an inch in length) which was embedded in the hole, probably exerted a greater transverse strain even than 8lbs. 8 ozs., for it had split the solid wood for a length of rather more than a quarter of an inch (exactly ·275 inch), and this fissure is shown in Fig. 55. A second stick was tried in the same manner with almost exactly the same result. We then followed a better plan. Holes were bored near Fig. 56. Wooden pincers, kept closed by a spiral brass spring, with a hole (' 14 inch in diameter and · 6 inch in depth) bored through the narrow closed part, through which a radicle of a bean was allowed to grow. Temp. 50°-60° F. the narrow end of two wooden clips or pincers (Fig. 56), kept closed by brass spiral springs. Two radicles in damp sand were allowed to grow through these holes. The |