. The elements of botany for beginners and for schools. Botany. 152 VEGETABLE LIFE AND WORK. [SECTION 16. in Locust-trees, in tlie Sensitive Plant (Fig. 100), and in Woodsorrel Young seedlings droop or close tlicir leaves at night in plants wliicli are not thus affected in tiie adult i'uliagc. All this is thought to be a protec- tion against the cold by nocturnal radiation. 470. Various plants climb by a coiling movement of their leaves or iheir leaf-stalks. Familiar examples are seen in Clematis, Maurandia, Troi)8eo- lum, and in a Solanum which is much cultivated in greenhouses (Fig. 172). In
. The elements of botany for beginners and for schools. Botany. 152 VEGETABLE LIFE AND WORK. [SECTION 16. in Locust-trees, in tlie Sensitive Plant (Fig. 100), and in Woodsorrel Young seedlings droop or close tlicir leaves at night in plants wliicli are not thus affected in tiie adult i'uliagc. All this is thought to be a protec- tion against the cold by nocturnal radiation. 470. Various plants climb by a coiling movement of their leaves or iheir leaf-stalks. Familiar examples are seen in Clematis, Maurandia, Troi)8eo- lum, and in a Solanum which is much cultivated in greenhouses (Fig. 172). In the latter, and in other woody plants which clind) in this way, tiie petioles thicken and harden alter they have grasped iheir support, thus securing a very firm hold. 471 • Tendril movements. Tendrils are either leaves or stems (98, 16S), specially developed for climbing purposes. Cobaea is a good exam- ple of partial transformation; some of the leaflets are normal, some of the same leaf are little tendrils, and some intermediate in character. The Passion-flowers give good examples of simple stem-tendrils (Fig. 92) ; Grape-Vines, of branched ones. Most tendrils make revolving sweeps, like those of twining stems. Those of some Passion-flowers, in sultry weather, are apt to move fast enough for the movement actually to be seen for a part of the circuit, as plainly as that of the second-hand of a watch. Two herbaceous species, Passiflora and P. sicyoides (the first an annual, the second a strong-rooted perennial of the easiest cultivation), are admirable for illustration both of revolving movements and of sensitive coiling. 472. Movements under Irritation. The mo.^t familiar case is that of the Sensitive Plant (Fig. 490). The leaves suddenly take their nocturnal position when roughly touched or when shocked by a jar. The leaflets close in pairs, the four outspread par- tial petioles come closer together, and the common petiole is depressed. The seat of the move- ments
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1887
