THE SPERMATOPHYTA 



357 



Reproduction. — The gyinnospenns are all wiud-pollinated, and 

 many of the lower angiospcrms resemble them in this respect and 

 have inconspicuous, cone-like reproductive organs (Fig. 107) often 

 not differing remarkably in general appearance and function 

 from the gymnosperm type, except in the possession of ovaries. 



C D 



Fig. 228. — The process of seed-production in a flowering plant. Longitudinal 

 diagrams of flower and fruit, the calyx and corolla solid black; the ovule, seed- 

 coats and embryo dotted, and the ovary wall, style and stigma lined. A, young 

 bud, the stamens and the single ovule beginning to develop. B, bud ready to 

 unfold. The embryo-sac within the ovule is fully developed and the egg (below) 

 and double endosperm nucleus (in center) are ready for fertilization. C, fully 

 opened flower. The anthers have burst and pollination has taken place, pollen 

 grains being transferred to the stigma. Two grains have germinated, and the 

 pollen-tube from one of them has penetrated the style, entered the ovary, passed 

 through the micropyle of the ovule and discharged its contents — the two male 

 gametes — into the embryo-sac. Double fertilization is taking place, one male 

 gamete uniting with the egg and the other with the endosperm nucleus. D, 

 ripe fruit. Sepals, petals and stamens have dropped off; the ovary wall has 

 hardened into the pericarp; the micropyle has closed; the integuments have 

 become seed coats and the ovule has developed into the seed. The embryo, in 

 the center of the seed, has grown from the fertilized egg, and the endosperm 

 surrounding it (shown in white) from the endosperm nucleus. 



The higher members, however, have come to depend upon 

 insects to transport their pollen, and have evolved the charac- 

 teristic flower (Fig. 227) which we have described in a previous 

 chapter, with its protective calyx, composed of sepals; its attrac- 



