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 umbellattts. A flower, the natural size. the gynaeceum after removal of the perianth and 

 the stamens, magnified ; n 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; zVthe integuments, K the nucellus, /f.Sthe raphe, em the embryo-sac, ^-"transverse section 

 through the stigmatic portion of a carpel highly magnified ; 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 

 ft at z. H part of a valve of the anther answering to /9 in G ; y the point where it has separated from the connective, e the 

 epidermis, x 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./; those of the inner/' are simple and thicker. The gynaeceum also consists of two whorls of three 

 members each, an outer c and an inner <?. 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. 



