474 ANGIOSPERMS less. 



the venter of the pistil (vnf) : it thus loses all appearance of 

 being a stem-structure and becomes a mere capsule for the 

 gynoecium, giving attachment at its edges to the other 

 floral organs. 



An extended study of flowers will show how all the main 

 modifications are brought about by the varying form of 

 the floral receptacle, by the concrescence of one part with 

 another, by the enlargement of certain parts, and by the 

 diminution or complete suppression of others. 



The microspores are at first simple cells, each with a 

 double cell-wall and a nucleus. The nucleus divides into 

 two (Fig. 126, d), a larger vegetative nucleus, and a smaller 

 which divides again forming two generative nuclei, each 

 surrounded by its layer of protoplasm. 



No prothallus is formed in the megaspore, but its nucleus 

 divides, the products of division pass to opposite ends of 

 the spore, and each divides again and then again, so that 

 four nuclei are produced at each extremity. Three of the 

 nuclei at the proximal end — that furthest from the micropyle 

 — become surrounded by protoplasm and take on the char- 

 acter of cells (d, a/i/) all devoid of cell-wall and called antipodal 

 cells ; the fourth remains unchanged. Similarly, of the four 

 nuclei at the distal or micropylar end, one remains unchanged 

 and three assume the form of cells by becoming invested 

 with protoplasm. Of these three, two lie near the wall of 

 the megaspore and are called synergidce {sng): the third, more 

 deeply placed, is the ovum {ov). The two unaltered nuclei 

 now travel to the centre of the megaspore and unite with 

 one another, forming the secondary nucleus {nu) of the spore. 



There is thus a single ovum produced in each megaspore, 

 but no ovary and no prothallus : the female portion of the 

 gamobium is reduced to its simplest expression. 



