384 



XXVIII. THE ANDR(ECIUM OF ANGIOSPERMS. 



140, C, e), of two or three layers of flat (/, c), and one layer 



of radially-elongated cells (t), the former the meso- and endo- 



thecium, the 

 latter the tape- 

 tal layer, 

 These last sur- 

 round the entire 

 sac. The in- 

 terior is filled 

 with polygonal 

 pollen mother- 

 cells, still co- 

 hering. If we 

 'next prepare 

 cross-sections 

 through a 

 flower - bud 

 about | inch in 

 FIG. 140. Hemerocallis fulva. A, cross-section through an height we shall 



almost ripe anther, with pollen-sacs opened by cutting ; p, the 



partition wall between the sacs ; /, vascular bundle of the see the pollen 



connective; a, groove along the connective (x 14). B, cross- 

 section through a young anther (x 28). C, Part of the previous 



mothe r-cells 



cross-section of a sac; e, epidermis ; /, the mesothecium, later already isolated 



forming the fibrous layer; c, the layer to be displaced (endo- / 



thecium) ; t, the tapetal layer, to be resorbed later on ; pm, and in course 



pollen mother-cells (x 240). JJ and E, division of the pollen ,. j- 



mother-cells (x 240). f division. 



These pollen 



mother-cells are recognisable by their white, thick, strongly- 

 refractive wall ; their contents are divided into two, or already 

 into four cells, which lie in one (Fig. 140, D), or in two planes 

 at right angles (Fig. 140, E). Pollen-grains, therefore, like 

 spores, are produced by quadri-partition inside their mother- 

 cells. The wall of the anther is lined by tapetal cells, which 

 are filled with yellow -brown contents. These constitute the 

 innermost layer (t) clothing the young sac. In slightly older 

 flower-buds the walls of the pollen mother-cells are dissolved ; 

 the young pollen-grains lie free ; the tapetal cells have for the 

 most part lost their individuality, their contents have penetrated 

 between the young pollen -grains. The layer of flattened cells 

 (/) underlying the epidermis has strongly developed, and forms 

 the fibrous layer, while the next inner layer is crushed and 

 disorganised. Ultimately, as still older buds show, the un- 

 consumed portion of the tapetal cells, especially in the periphery 



