. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. HYDATHODES 147 above the bundle-end breaks down completely, so that the escaping water passes directly to the exterior. Hydathodes can often be recognised at a very early stage, and are probably most active in the young leaf, which develops in an almost saturated atmosphere within the expanding bud. Active secretion of water takes place when the hydrostatic pressure within the plant becomes excessive, that is when trans- piration is slow and absorption considerable, a condition that is most frequently attaine
. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. HYDATHODES 147 above the bundle-end breaks down completely, so that the escaping water passes directly to the exterior. Hydathodes can often be recognised at a very early stage, and are probably most active in the young leaf, which develops in an almost saturated atmosphere within the expanding bud. Active secretion of water takes place when the hydrostatic pressure within the plant becomes excessive, that is when trans- piration is slow and absorption considerable, a condition that is most frequently attained at night, but which can be artificially produced by placing a well-watered plant under a beU-jar in a warm room.^ The hydathodes can therefore be regarded as safety-valves which avert blocking of the intercellular spaces. Fig. 73.—Hydathode of Lesser Celandine (Ficaria verna) in vertical section (after Salisbury), ep., epithcm tissue ; St., water-pores. with water under the conditions just mentioned. In the case of the semi-parasites they probably serve to get rid of the water which is absorbed in excess from the host. The liquid exuded from hydathodes is not pure water, but usually contains a very small percentage of dissolved salts. In some cases, however, the amount of the latter may be so considerable that they remain behind as an incrustation when the water evaporates. Thus in the Saxifrages {Saxifraga) a little white scale consisting of carbonate of lime forms on the leaf-teeth over each of the hydathodes. The exudation of water from the hair-like hydathodes of semi-parasites and the Runner Bean is due to active secretion on the part of the protoplasts of the constituent cells. As a 1 Cf. F. & S., p. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Fritsch, Felix Eugene, 1879-; Salisbury,
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectpl, booksubjectplants
