22 8 THE PHYSIOLOGY OF PLANTS 



way down through a special conducting tissue (/) into the 

 cavity of the ovary, and then through the micropyle (m) of the 

 ovule. The more detailed representation of these processes 

 is shown in the subsequent figure (Fig. 32). In the preceding 

 one we were chiefly concerned with the general position of the 

 ovule in the ovary, at the side of which a young stamen (st) is 

 represented, and the figure was also intended to illustrate the 

 delicate and feathery structure of the stigma. 

 . The actual process of fertilisation in the receptive ovule 

 is represented (after Kny) in the case of the ovule of the 

 Pansy (Viola tricolor). The ovule has been detached from the 

 ovary wall at the point 'p, the placental reg-ion, which pro- 

 duced the ovule. The vascular bundle (r) of the placenta 

 is continued for the purposes of nutrition into the base of 

 the ovule. The tissue in which it terminates in the ovule 

 has been termed the chalaza. The nueellus is enclosed by 

 the inner integument {J J) and the outer integument {A J), 

 which however leave the small canal or micropyle open. The 

 pollen tube has penetrated into this passage, has grown through 

 the apex of the nueellus (I^Jl^ towards a large and almost 

 cylindrical cell, the embryo sae. 



The embryo sac has become developed from one of the cells 

 of the nueellus by considerable eulargement at the expense of 

 the neighbouring cells, which broke down into mucilage. It 

 contains at the commencement a large nucleus, which divides, 

 the daughter-nuclei progressing to the two extremities of the 

 embryo sac. There, by repeated division, a group of four nuclei 

 results. A later stage of development is shown in the case of 

 the embryo sac of Polygonum divaricatum (Fig. 3 3 , after Stras- 

 burger). Two of the cells (s) at the apex of the embryo sac 

 exhibit each a large vacuole and towards the apex a nucleus ; 

 the third one (e) has the nucleus at the base and the vacuole 

 at the apex. 



It is only this latter cell, the egg-cell, which gives rise 

 after fertilisation to the young plant (emhri/o). The other two 

 cells, characterised by the striped appearance they represent, 

 have been termed the synergidse. The group of three cells 

 is called the egg apparatus. 



The cells at the opposite end of the embryo sac are sur- 



