Elementary botany . tic tundra. 2d. Sand * strand of beach. The quantityof sand with very little or no admixture of humus or plant foodmakes it difficult for plants to obtain a sufficient amount of * See Chapter LIV of the authors College Text-book of Botany. 4$4 RELATION TO ENVIRONMENT. water even where rainfall is abundant. The same may be saidof the sand dunes farther back from the shore. The plantsof these areas are then usually xerophytes. Some of the plantsaccustomed to growing in such localities are American sea-rocket,seaside spurge, bugseed, sea-blite, sea-purslane, the sand-cherry, d
Elementary botany . tic tundra. 2d. Sand * strand of beach. The quantityof sand with very little or no admixture of humus or plant foodmakes it difficult for plants to obtain a sufficient amount of * See Chapter LIV of the authors College Text-book of Botany. 4$4 RELATION TO ENVIRONMENT. water even where rainfall is abundant. The same may be saidof the sand dunes farther back from the shore. The plantsof these areas are then usually xerophytes. Some of the plantsaccustomed to growing in such localities are American sea-rocket,seaside spurge, bugseed, sea-blite, sea-purslane, the sand-cherry, dwarf willow, marram-grass, certain species of beard-grass, etc. 3d. Rocky shores or areas. Here lichens and mossesfirst grow, later to be followed by herbs, grasses, shrubs, andtrees, as decayed plant remains accumulate in the rock Shores of ponds, or swamp moors. Here the vegetationoften takes on a zonal arrangement if the ground graduallyslopes to the shore and out into the pond. In Fig. 493 is shown. Fig. 493-Macrophytes in the upper zone of the photic region. Ascophyllum and Fucusat low tide, Hunters Island, New York City. (Photograph by M. A. Howe.) zonal distribution of plants. The different kinds of plants aredrawn into these zones by the varying amount of ground waterin the soil, or the varying depth of the water on the margin ofthe pond as one proceeds from the land towards the deeperwater. On the border lines or tension lines between the differentzones the plants are struggling to occupy here ground which issuitable for each adjacent individual formation. Other edaphicsocieties are those of marl ponds, alkaline areas, oases in deserts, PLANT SOCIETIES. 485
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