FERTILISATION AND ITS EFFECTS 273 



the centre, and fuse with each other to form what is termed 

 the secondary or definitive nucleus of the embryo-sac {h, Fig. 99). 

 The three nuclei at the end of the embryo-sac farthest away 

 from the micropyle become surrounded with a certain amount 

 of cytoplasm and then develop cell-walls ; the cells produced 

 are termed antipodal cells («). At the end nearest the micropyle 

 the nuclei and associated cytoplasm remain without cell-walls 

 and constitute what is known as the egg-apparatus ; two of these 

 three cells are termed synergidce, the third being known as the 

 ovum, egg-cell or oosphere {e). The ovum is the special female 

 reproductive cell of the plant which after fusion with the male 

 reproductive cell of the pollen-grain, begins a new life as it were, 

 and develops into a new plant. 



Ex. 166. — Tease out with needles the ovules fiotn the ovaries of the recently 

 opened flowers of pea, bean, tulip, and others of similar size ; mount in a drop 

 of water and examine with -a. low power, noting if possible the funicle and 

 position of the micropyle. 



Ex. 167. — Cut transverse sections of these ovaries ar,d mount the sections 

 in a 1 per cent, solution of caustic potash. Observe and sketch under a low 

 power the form, structure and attachment of the ovules to the carpels. 



Ex. 168. — Place some flowers of marsh marigold (Caltha palustris L.) 

 which have just opened in methylated spirit. After hardening a few daj 5 

 strip off the petals and stamens and cut a number of transverse sections 

 through the carpels «'ith a razor wetted with the spirit ; many of the sections 

 will also pass through the ovules within the carpels. Transfer the sections 

 into a watch glass containing a mixture of equal parts of methylated spirit 

 and glycerine. Now pick out one or two sections which appear to have 

 passed through the ovules and mount them in a drop of pure glycerine. 



I. Examine and sketch under a low power, noting — 

 (i) The section of the wall of the carpel ; 



(2) The anatropous ovule and its funicle ; 



(3) The large embryo-sac. 



z. Examine and sketch the embryo-sac under a high power, noting 

 within it — 

 (i) The central definitive nucleus ; 



(2) The antipodal cells at one end ; and 



(3) The ovum and synergidse at the other. 



4. Fertilisation and its effects. — When a pollen-grain is placed 



s 



