ANGIOSPERMS. 



483 



several layers, the future wall of the pollen-sac (Fig. 343, A). The innermost layer, 

 which is continued round the whole mass of mother-cells, is transformed at an early 



Fig 346.— -4 pollen-sa: of Althaa rosea seen from the side ; B transverse section of an anther-lobe showing the 

 two pollen-sacs, m the mother-cells of the pollen, in A still united into a tissue, in 5 already divided each Into four -'; 



pollen-cells, n the epithelium of the pollen-sac. Each anther-lobe, consisting of two pollen-sacs, is here borne on 

 a long branch of the filament. 



period into a delicate thin-walled epithelium {ep) filled with coarse-grained protoplasm, 

 the cells of which usually divide radially and elongate, but are afterwards destroyed 



Fig 347 —AltJuEa rosea ■ A^E division of the mother-cells of the pollen into four ; /^ and G a tetrahedron, the 

 walls of whose special mother-cells have burst under the influence of water, and have allowed the protoplasmic body 

 of the young pollen-cells to escape ; H a mature pollen-grain seen from without magnified to the same extent 

 (C/t Fig. II, p. 14). 



like the inner layer of cells in the sporangium of Vascular Cryptogams. The de- 

 velopment of the outer cell-layers which subsequently cause the rupture of the wall 



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