. Plant studies; an elementary botany. Botany. XEKOPHYTE ASSOCIATIONS 203. stands in the water its stem is exposed to a heat which is often intense. The ordinary prairie (see §146) is included among mesophyte associa- tions on account of the rich, well- watered soil; and yet many of the plants are very xerophytic in struc- ture, probably on account of the pre- vailing dry winds. The ordinary sphagnum-bog (see §132), or " peat-bog," is included among hydrophyte associations, It has an abundance of water, and is not exposed to blazing heat, as in the case of the bulrushes, or to drying
. Plant studies; an elementary botany. Botany. XEKOPHYTE ASSOCIATIONS 203. stands in the water its stem is exposed to a heat which is often intense. The ordinary prairie (see §146) is included among mesophyte associa- tions on account of the rich, well- watered soil; and yet many of the plants are very xerophytic in struc- ture, probably on account of the pre- vailing dry winds. The ordinary sphagnum-bog (see §132), or " peat-bog," is included among hydrophyte associations, It has an abundance of water, and is not exposed to blazing heat, as in the case of the bulrushes, or to drying wind, as in the case of prairie plants; and yet its plants show a xerophytic struc- ture. The cause for this has not yet been determined, although several suggestions have been made. It is evident, therefore, that xero- phytic structures are not necessarily confined to xerophytic situations. It is probably true that all associations which show xerophytic structures belong to- gether more naturally than do the associa- tions which are grouped according to the water supply. Fig. 182. Cells from the leaf of a quillwort (Isoetes). The light is striking the cells from the direction of one looking at the illus- tration. If it be some- what diffuse the chloro- plasts distribute them- selves through the shal- low cell, as in the cell to the left. If the light be intense, the chloroplasts move to the wall and as- sume positions less ex- posed, as in the cell to the right. Associations No attempt will be made to classify these very numerous associa-. 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 Coulter, John Merle, 1851-1928. New York, D. Appleton and Company
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