37 



FOURTH GROUP. SEED-PLANTS. 



it is obvious that there can be no scattering of pollen-dust, nor can the pollen-masses 

 fall of themselves out of the anthers ; the parts of the flower are disposed in special 

 ways to cause honey-seeking insects to draw the pollinia or the coherent pollen-masses 

 from the pollen-sacs, and to deposit them on the stigma of other flowers of the same 



species. 



The gynaeceum 1 of the Angiosperms consists of one or more closed chambers 

 in which the ovules are formed ; the lower hollow enlarged portion of the chambers, 

 which encloses the ovules, is called the ovary ; the spot or the mass of tissue from 

 which the ovules immediately arise in the ovary is a placenta. Above the ovary the 



FIG. 299. Butomus umbellatits. A flower, the natural size. B the gynaeceum after removal of the perianth and 

 the stamens, magnified ; the stigmas. C transverse section through three of the monomerous ovaries, each carpel 

 bearing on its inner surface a number of ovules. D a young ovule ; i commencing integument. E a similar one imme- 

 diately before fertilisation ; ii the integuments, K the nucellus, KS the raphe, em the embryo-sac. F transverse section 

 through the stigmatic portion of a carpel highly magnified j pollen-grains are attached to the hairs of the stigma. 

 G transverse section of an anther which is quadrilocular, but afterwards appears bilocular by the separation of the valves 

 /8 at a. H part of a valve of the anther answering to ft in G ; y the point where it has separated from the connective, e the 

 epidermis, AT the fibrous cell-layer (endothecium). /diagram of the whole flower; the perianth // consists of two alterna- 

 ting whorls of three members each, the androecium of the same number of whorls, but the stamens of the outer whorl 

 are doubled f, those of the inner y are simple and thicker. The gynaeceum also consists of two whorls of three 

 members each, an outer c and an inner c'. There are present therefore six alternating whorls of three members, the 

 members of the first whorl of stamens being doubled. 



chamber narrows into one or more slender stalk-like formations, the styles, which bear 

 the stigmas ; these are glandular swellings or expansions of varying shape, which 

 retain the pollen conveyed to them and stimulate it by the moisture which they 

 secrete to put forth the pollen-tubes. 



1 The views of Payer, which differ in some important points, should be compared with the text ; 

 see his Organogenic de la fleur, p. 725. 



