Plants and their ways in South Africa . hich have just germinatedby means of a narrow strip of flannel to the upper edge of the the flannel moist, and the roots will follow the inclined face of thegerminator instead of growing vertically. The flannel must not be toomoist, or the roots will turn from it. Ex. 8. Growth Curvatures caused by Light.—Place the germinatorin a box lighted at one end. Notice the seedlings in a day or so. Thestems will bend towards the lighted end. Will the roots show a turningaway from the light ? The seedlings of sunflower are very sensitive to light. Place
Plants and their ways in South Africa . hich have just germinatedby means of a narrow strip of flannel to the upper edge of the the flannel moist, and the roots will follow the inclined face of thegerminator instead of growing vertically. The flannel must not be toomoist, or the roots will turn from it. Ex. 8. Growth Curvatures caused by Light.—Place the germinatorin a box lighted at one end. Notice the seedlings in a day or so. Thestems will bend towards the lighted end. Will the roots show a turningaway from the light ? The seedlings of sunflower are very sensitive to light. Place some ina bright light and cover with black paper, leaving an opening at one how the cotyledons turn their flat surfaces to the light. As soonas the next pair of leaves appear, reverse the position, so that they turndirectly away from the light. Will they turn back ? Try the experimentwith other seedlings. Fig. 29 shows a young castor-oil plant. All the leaves, in-cluding the cotyledons, have turned toward the window. The. Fig. 30.—The plant in this pot grew on the north side of a large portion beside the pot grew on the south side in the shade. stalks {petioles) of the cotyledons have curved so as to bringthe surface of the cotyledons into a favourable light position. Growth of Roots^ Stems, and Leaves 23 Ex. g. The cotyledons of the bean have no petioles. On the stem ofthose which are turned away from the light, below the cotyledons, makea row of ink marks. Place in a lighted window. In a day or so thecotyledons will look toward the light. The row of marks will show thatthe stem has twisted to bring them into position; When growth in thatportion of the stem has stopped, turn the plant halfway around. Will thecotyledons again turn toward the light ? Ex. 10. Remove the tips from sunflower seedlings, cutting off someabove and some below the cotyledons. Do the stems still curve towardthe light ? Ex. II. Plant sunflower seeds and keep them covered so as to
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectplants, bookyear1915
