DEVELOPMENT OF POLLEN-GRAINS. 427 



who made a special study of it. " The contents of each of these 

 cells secrete a layer of cellulose, which does not adhere to the 

 wall of the parent-cell to form a layer of secondary deposit, but 

 lies free against it, so that a new free cell is formed within each 

 old one, nearly filling it. The walls of the old cells then dissolve, 

 so that the free cells become free, no longer in their parent-cells, 

 but in a cavity which is to constitute the pollen-chamber or loculus 

 of the anther. These free cells are the ' parent-cells of the pollen ' 

 of authors. A new phenomenon soon occurs in these. These 

 parent-cells divide into four by ordinary cell-division ; either by 

 one or two successive partings, by septa at right angles to each 

 other, but both perpendicular to an imaginary axis (as when 

 an orange is quartered) ; or by simultaneously formed septa, 

 which cut-off portions in such a manner, that the new cells 

 stand in the position of cannon balls piled into a pyramid 

 (tetrahed rally). These new cells are the 'special parent-cells of 

 the pollen ; ' and in each of these the entire protoplasmic contents 

 secrete a series of layers, which, in the ordinary course, by the 

 solution of the primary walls of the special parent-cells upon which 

 they were applied, become the walls of free-cells, which constitute 

 the simple ordinary pollen-cells. These subsequently increase in 

 size, and their outer coat assumes its characteristic form and 

 appearance, while free in the chamber of the anther."* This 

 history bears a very close parallel with that of the development of 

 the spores within the Theca of Mosses (§ 277) ; and it is not 

 a little curious that the layer of cells which lines the Pollen 

 Chambers should exhibit, in a considerable proportion of Plants, 

 a strong resemblance in structure, though not in form, to the 

 Elaters of Marchantia (Fig. ISO). For they have in their interior 

 a Fibrous deposit ; which sometimes forms a continuous spiral (like 

 that in Fig. 206), as in Narcissus and Hyosciamus ; but is Often 

 broken-up, as it were, into rings, as in the Iris and Hyacinth ; in 

 many instances forms an irregular net-work, as in the Violet and 

 Saxifrage ; in other cases, again, forms a set of interrupted arches, 

 the fibres being deficient on one side, as in the Yellow Water-lily, 

 Bryony, Primrose, &c. ; whilst a very peculiar stellate aspect is 

 often given to these Cells, by the convergence of the interrupted 

 fibres towards one point of the cell-wall, as in the Cactus, Gera- 

 nium, Madder, and many other well-known plants. Various inter- 

 mediate modifications exist ; and the particular form presented 

 often varies in different parts of the wall of one and the same 

 anther. It seems probable that, as in Hepatica?, the elasticity of 

 these Spiral Cells may have some share in the opening of the 

 Pollen-Chambers and in the dispersion of the Pollen-Grains. 



318. The form of the Pollen- Grains seems to depend in part 

 upon the mode of division of the cavity of the parent-cell into 



* " Micrographic Dictionary," 2nd Edition, p. 558. 



