. Gray's school and field book of botany. Consisting of "Lessons in botany," and "Field, forest, and garden botany," bound in one volume. Botany; Botany. 104 STAMENS. [SECTION 9. 297. An ordinary poilen-grain has two coats; the outer coat thickish, but weak, and frequently adorned with lines or bands, or studded with points; the inner coat is extremely thin and deKcate, but extensible, and its cavity when fresh contains a thickish protoplasmic fluid, often rendered turbid by an immense number of minute particles that float in it. As the pollen matures this fluid usually dri
. Gray's school and field book of botany. Consisting of "Lessons in botany," and "Field, forest, and garden botany," bound in one volume. Botany; Botany. 104 STAMENS. [SECTION 9. 297. An ordinary poilen-grain has two coats; the outer coat thickish, but weak, and frequently adorned with lines or bands, or studded with points; the inner coat is extremely thin and deKcate, but extensible, and its cavity when fresh contains a thickish protoplasmic fluid, often rendered turbid by an immense number of minute particles that float in it. As the pollen matures this fluid usually dries up, but the protoplasm does not lose its vitality. When the grain is wetted it absorbs water, swells up, and is apt to burst, discharging the contents. But when weak syrup is used it absorbs this slowly, and the tough in- ner coat will sometimes break through the outer and begin a kind of growth, like that which takes place when the pollen is placed upon the stigma. 398. Some pollen - grains are, as it were, lobed (as in Fig. 315, 316), or formed of four grains united (as in the Heath family. Eg. 317) : that of Pine (Fig. 318) has a large rounded and empty bladder-like expansion upon each side. This renders such pollen very buoyant, and capable of being trans- ported to a great distance by the wind. 299. In species of Acacia simple grains lightly cohere into globular pellets. In Milkweeds and in most sis 320 Orchids all the poUen of an anther-cell is compacted or coherent into one mass, called a Pollen-mass, or PoLLiNiUM, plural PoLLiNiA. (Fig. 819-332.) ing Primrose, the three lobes as large as the central body; 317, of Kalmla, four grains united, as in most of the Heath family; 318, of Pine, as it were of three grains or cells imited; the lateral empty and light. Fig. 319. Pollen, a pair of poUinia of a Milkweed, Asclepias, attached by stalks to a gland; moderately magnified. Pig. 320. PoUinium of an Orchis (Habenaria), with its stalk attached to a sticky gland; magnified.
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1887
