204 BOTANY FOR BEGINNERS CHAP. 



SUMMARY. 



The floral whorls are developed in the following order 



The calyx. The anterior sepal appears first, next the lateral, and 

 finally the posterior sepal. 



The corolla. All the petals appear together. 



The stamens. The anterior pair appear first, next the lateral pair, 

 and finally the posterior pair. 



The pistil. The carpels appear together. 



The sepals resemble foliage leaves in structure and appearance. They 

 protect the essential organs from injury, and if petaloid may attract 

 insects. 



The petals differ from foliage leaves in colour and texture. Their 

 principal function is to protect the essential organs, and by their shape, 

 colour, and perfume to attract insects. 



The essential floral organs consist of andrcecium and gyncecium. 

 These are essential for the production of seeds. The andrcecium pro- 

 duces pollen, and the gyncecium ovules. 



The structure of the androecium. It consists of modified leaves, 

 bearing very little resemblance, however, to foliage leaves. Its 

 function is to produce pollen and liberate it. The filament of an 

 anther represents the petiole of a foliage leaf and the anther lobes the 

 blade. 



The anther consists of the following layers of cells 



(a) The epidermis ; (b} the fibrous layer ; (c) the vascular bundle ; 

 (d) the tapetum layer, which generally disappears during the development 

 of the pollen ; (e) the pollen sacs. 



The development of pollen takes place in the pollen sacs. The 

 mother pollen cells divide up to form four daughter cells the pollen 

 grains. 



This division takes place in the following way 



(a) The nucleus divides into two ; (b) the two nuclei divide into 

 two each ; (c] the protoplasm becomes rounded off to form four cells 

 round the protoplasm ; (d) the mother cell-wall becomes disorganised 

 and the daughter cells are set at liberty as pollen grains. 



The pollen grain consists of a cell-wall, the outer part of which is 

 cuticularised to form the extine ; the inner, or intine, is very delicate 

 and consists of cellulose. The interior of the grain contains 



(a) A large nucleus the vegetative one ; (b) a small nucleus the 

 generative one. These are embedded in the protoplasm. 



The anther may liberate its pollen (a) by longitudinal slits, when the 

 dehiscence is longitudinal ; (b} by pores, when the dehiscence is porous ; 

 (c) by valves, when the dehiscence is valvular. 



The gyncecium is built up of carpels. Each carpel is a modified 

 leaf, and it consists of 



(a) The epidermis ; (b) mesophyll ; (c) vascular bundles. The 

 carpel may contain ovules. 



The parts present in an ovule are 



(a) The funiculus or stalk ; (b) the integuments or coverings of the 

 ovules ; (<) the nucellus in which (d] embryo-sac is embedded. 



