THE AXGIOSPERMAE 



1361 



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Fig. 1266. — Lilium catuiidiim. Meiosis in the microspore mother cells. A, Early metaphase, 

 metaphase and anaphase of meiosis I, showing lack of synchrony. B, Metaphase and 

 early telophase of meiosis II. C, Telophase and internal wall formation at end of 

 meiosis II. D, Transverse section of a loculus with cellular tapetum and tetrads mostly 

 completed. 



Dicotyledons. At the same time the anther enlarges markedly so that the 

 mass of sporogenous cells is separated from the anther wall and the pollen 

 loculus becomes visible as a space. When the mother cells divide, a tetrad 

 group of haploid cells results, usually arranged in a tetrahedron but some- 

 times all in one plane (Orchidaceae). The difference depends upon whether 

 the axis of the second meiotic division is at right angles to that of the first 

 division (tetrahedral) or parallel to it (one plane). The mother cell wall 

 remains, enveloping the tetrad, and becomes massive and mucilaginous, 

 containing callose and pectose. Within this general wall is another wall, also 

 mucilaginous, and containing callose and pectose, which surrounds each 

 cell of the tetrad and constitutes the "special wall", or "special mother 



