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A TEXTBOOK OF THEORETICAL BOTANY 



Fig. 1265. — Riimex crispiis. A, Archesporial cells in young anther. B, 

 Primary sporogenous and primary parietal cells. C, Pollen mother 

 cells, tapetum and parietal layers developed. (After Dudgeon.) 



below ground, as in plants with bulbs and corms, development may go on 

 slowly during the winter, even when the soil is frozen, so that the pollen 

 is mature before the spring growth begins, but in most cases the anthers 

 appear to pass the winter in the mother cell condition. Of course this does 

 not hold good for annuals and other summer-flowering plants, but even in 

 them, although development is continuous, there is a short pause at the 

 mother cell stage. 



The development of the microsporangia in the anther is usually well in 

 advance of the development of the megasporangia in the ovules or even in 

 advance of the development of the ovules themselves. Indeed in Quercus, 

 Ulmiis and some Orchidaceae, the pollen is not only formed but liberated 

 and pollination has taken place before the ovules are formed. 



The division of the pollen mother cell is, of course, the reduction divi- 

 sion, the special features of which we shall deal with in a future chapter (see 

 also Volume I, p. 29) (Fig. 1266). At present we are concerned with the 

 cells rather than with the chromosomes. Before division the walls of the 

 mother cells increase in thickness, somewhat unequally at different points 

 round the cell, and the thickened walls show concentric lamellation. In 

 most Monocotyledons the middle lamellae between them dissolve and the 

 cells separate and become rounded but this does not usually happen in 



