. A textbook of botany for colleges and universities ... Botany. 1142 1143 1144 Figs. 1142-1144. — Stamens of angiosperms, showing methods of anther dehiscence: 1142, ordinary stamens with longitudinal dehiscence; 1143, o. stamen of Solanum with dehiscence by a terminal slit or pore; 1144, a stamen of Vaccinium with tubular prolongations of the pollen sacs. — From Kerner. in the Ericaceae, figs. 1143, T144). Dehiscence is occa- sioned by tissue desiccation. Beneath the epidermis is a layer with unequally thick- ened fibers, in which strains arise when the water content lessens; rupture then oc
. A textbook of botany for colleges and universities ... Botany. 1142 1143 1144 Figs. 1142-1144. — Stamens of angiosperms, showing methods of anther dehiscence: 1142, ordinary stamens with longitudinal dehiscence; 1143, o. stamen of Solanum with dehiscence by a terminal slit or pore; 1144, a stamen of Vaccinium with tubular prolongations of the pollen sacs. — From Kerner. in the Ericaceae, figs. 1143, T144). Dehiscence is occa- sioned by tissue desiccation. Beneath the epidermis is a layer with unequally thick- ened fibers, in which strains arise when the water content lessens; rupture then occurs along the Unes (or at the spots) of weakness, where- upon the pollen may be shaken out by such agents as wind and insects. Commonly anther desiccation is due to the great transpiration to which open flowers are exposed. Some anthers, however, open in the bud or in moist weather and it has been claimed that this is due to the absorption of water from the anther by adjoining nectaries or by other tissues rich in sugar. Dehiscence occurs when anthers are placed in contact with a cane sugar solution, though much more slowly than in dry air. Light and the pressure of growing pol- len also appear to facilitate dehiscence. The pollen. — The pollen grains are borne in pollen sacs within the anther, where they com- monly are produced in fours {tetrads). Usually the grains break apart at maturity, scattering in- dependently, but in some plants they cohere in groups (as in Mimosa), while in others they cohere in large and defi- nite masses, known as pollinia (as in the milk- (exine); highly magnified. — From 1143 1147 Figs. 1145-1148. — Different stages of pollen grain development in a rosin-weed (Silphium): 1145, a micro- spore, representing the one-celled stage of a developing pollen grain; 1146, a mature pollen grain; 1147, 1148, germinating pollen grains, shoving the first stages of pol- len tube development; note the thick and spiny outer coat. Please note th
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