. Fresh-water biology. Freshwater biology. 192 FRESH-WATER BIOLOGY. the Nymphaeaceae large tubers are common and young plants of Nymphaea alba may sometimes be found floating about attached to a tuber. The swamp plants, such as Typha and Scirpus, also have exten- sive rhizome systems which are important means of wintering and acquiring new territory. Some plants have winter buds or hibernacula which form in autumn, separate from the parent plant, often drift to a new locahty, and finally sink to pass the winter in a dormant condition only to commence a new generation the following spring (Fig.
. Fresh-water biology. Freshwater biology. 192 FRESH-WATER BIOLOGY. the Nymphaeaceae large tubers are common and young plants of Nymphaea alba may sometimes be found floating about attached to a tuber. The swamp plants, such as Typha and Scirpus, also have exten- sive rhizome systems which are important means of wintering and acquiring new territory. Some plants have winter buds or hibernacula which form in autumn, separate from the parent plant, often drift to a new locahty, and finally sink to pass the winter in a dormant condition only to commence a new generation the following spring (Fig. 269). Such winter buds are commonly formed by Utricularia, Potamogeton crispus, P zosterifo- lius, P. pusillus, , and possibly others. The sinking of those winter buds may be ac- complished by the intercellular spaces becom- ing injected with water, as is the case with the autumn plants of Lemna minor. Aside from special organs of propagation quite a few plants acquire new stations by means of the fragments of vegetative parts accidentally set adrift. It is common to find floating stems of Elodea, from the nodes of which adventitious roots have risen. These roots grow straight downward and the stem makes Httle growth in length while the roots are seeking the soil. A fragment of Elodea was found floating in Lake Erie which had an adventitious unbranched root 45 cms. in length. The roots do not branch in some species until the soil is penetrated and then a system of lateral branches develops to anchor the plant. In Potamogeton perfoliatus the adventitious roots usually arise from the nodes of new rhizomes which develop in the leaf axils of the cutting. With land plants the development of roots on the seedling is as marked as the growth of stem and leaves, but in several water plants the root development is subordinated to that of the stem and leaves, while in some species a genuine functional root is not developed. The rudiment of a root may be present as a part of Fig.
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectfreshwa, bookyear1918
