. Plant studies; an elementary botany. Botany. KOOTS 95. tern, as if seeking for -n-ater and tlie essential materials. Sometimes the root system Ijeeomes ;ly extensive, visiting a large amount of soil in order to iirocuro the necessary suiiplies. Sometimes the soil is poor in heat, and root activity is interfered with. In sncli cases it is very common to find the leaves massed against the soil, tliiis slightly checking the loss of heat. Most Soil roots also need free air, and when water covers the soil the supply is cut off. In many cases there is some way by which a supplj- of fre
. Plant studies; an elementary botany. Botany. KOOTS 95. tern, as if seeking for -n-ater and tlie essential materials. Sometimes the root system Ijeeomes ;ly extensive, visiting a large amount of soil in order to iirocuro the necessary suiiplies. Sometimes the soil is poor in heat, and root activity is interfered with. In sncli cases it is very common to find the leaves massed against the soil, tliiis slightly checking the loss of heat. Most Soil roots also need free air, and when water covers the soil the supply is cut off. In many cases there is some way by which a supplj- of free air may lie brought down into the roots from the parts above water ; sometimes by large air passages in leaves and stems (see Figs. H7. 88. 80, 00) ; some- times by developing sjiecial root structures which rise above the water level, as iirominently shown Ijy the cypi-ess in the development of knees. These knees are outgrowths from roots beneath the water of the cypress swamp, and rise above the water level, thus reaching the air and aerating the root system (see Fig. 01). It has been shown that if the water rises so high as to flood the knees for any lengtli of time the trees will die, but it does not follow that this is the chief reason for their development. 65. Water roots.—A very different type of root is devel- oped if it is exposed to free water, without any soil relation. If a stem is floating, clusters of whitish thread-like roots usually put out from it and dangle in the water. If the water level sinks so as to bring the tips of these roots to the mucky Fil;. 90. Lnngitmlinal SL-ction throuizh il yonn^f qiiillwort k'af, showing that the four air cham- Ijers shown in Fig. 80 are not con- tinuous passages, luit that tlu're are four \erlica] ro\\s of promi- nent chambers. Tlie plates of cells separating the chambers in a vertical row very soon become dead and full of air. In addition to the work of aeration these air chambers are very serviceable in enabling the lea
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbotany, bookyear1900
