454 BOTANY 



of the floral leaves are most clearly represented by means of diagrams 

 or formulae. The manner in which such diagrams may be constructed 

 has previously been explained (p. 39). la a floral formula the 

 single whorls are indicated by letters, the number of their members by 

 corresponding figures, or, when their number is large or indefinite, 

 by oo . The union of parts is expressed by ( ), superior and inferior 

 ovaries by a line above or below the corresponding figure, zygomorpbism 

 byf. 



Of the letters employed in such formulae, K = calyx, C = corolla, 

 P = perigone, A = andrcecium, G = gynoecium. The following are ex- 

 amples of floral formulae. 



Lily . . . . P3 + 3, A3 + 3, G (3). 



Buttercup K 5, C 5, A a , G » . 



Apple Blossom . K 5, C 5, A oo , G (5). 



. . f K 5, C 5, A 4, G (2). 



Fertilisation and its Results 



The Sexual Generation. — The male prothallium of the Angio- 

 sperms, like that of the Gymnosperms, consists of a small antheridial 

 and a large vegetative cell, not separated, however, by a partition wall 

 (Fig. 3S6). The antheridial cell divides ultimately into two naked 

 generative cells. 



The ovule contains one embryo-sac, very rarely more. Within the 

 embryo-sac only six cells are produced, and not, as 

 in the Gymnosperms, an enclosed tissue consist- 

 ing of numerous cells. These six cells, which 

 remain naked until fertilisation takes place, 

 arrange themselves in two groups at the poles 

 of the embryo- sac, each group consisting of three 

 cells. 



The group of three cells at the micropylar end 



of the embryo-sac constitutes the egg-APPAKATUS 



fig. 3S6. — Tmdcscantia (Fig. 387). It comprises the EGG-CELL and two 



£ta "aft"; dltion SYNERGIM, so designated because, although 



into an antheridial remaining sterile, they are apparently of assistance 



and vegetative ceil. j n tne fertilisation of the egg-cell. The cells at 



(X 540 ) 



the other pole of the embryo-sac fulfil no apparent 

 function. They are termed ANTIPODAL CELLS. 



Egg-apparatus and antipodal cells are together regarded, probably correctly, as 

 a very reduced prothallium, homologous with the undoubted prothallium developed 

 in the embryo-sac of Gymnosperms. In support of this view, however, there is as 

 yet no phylogenetic evidence. The development of the cells takes place somewhat 

 as follows. 



