418 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS. 



phj^siology is now so active that many matters once regarded as settled have come 

 to the front again as open questions. 



In the GyTTinosperms, the group of Flowering Plants with exposed ovules, 

 though the essential facts of fertilization — the fusion of the male sexual cell with 

 the female sexual cell (egg) — are the same as in the AngiospevTns, just described, 

 in many subordinate points they exhibit marked differences. The male flowers of 

 Gymnosperms produce stamens with anthers in which pollen-grains are developed 

 much as in Angiosperms. The arrangements, however, associated with the produc- 

 tion of ovules are simpler than in the Angiosperms, and recall to some extent the 

 characters presented by certain Ferns. In the Ferns and other Cryptogams it will 

 be remembered that fertilization is under water, whilst in Phanerogams this is 

 accomplished through the medium of the air (c/. p. 71). The spermatozoids of the 

 Cryptogams reach the egg-cell in the oogonium or archegonium by swimming; they 

 are naked protoplasmic masses, and need no enveloping and protective cell-wall. It 

 is otherwise in the Phanerogams, where aerial fertilization obtains. Here a mem- 

 brane around the spermatoplasm is of great value; it serves to protect the contents 

 of the pollen-grain during its journey through the air, and afterwards, in connection 

 with the pollen-tube, is of the utmost value in conveying the male sexual cell to the 

 egg. It is interesting to note, however, that in certain Fern-like Gymnosperms, i.e. 

 in Cycads, and in Ginkgo, although pollen-tubes are produced, they do not reach 

 to the egg-cell, but liberate motile spermatozoids which swim the last bit of the 

 way. Cryptogamic methods are thus retained in the most primitive Gymnosperms. 



The ovules of Gymnosperms show the grosser characters of those of Angiosperms. 

 In fig. 335 ^ is shown a scale from a female flower (cone) of the Scotch Pine {Pinus 

 sylvestris). Right and left at its base are the ovules, two in number. Each ovule 

 exhibits a central nucellus and a conspicuous integument surrounding it, leaving a 

 wide, funnel-shaped micropyle giving access to the tip of the nucellus (c/. also fig. 

 208^, p. 74, representing an ovule of Cycas). Within the nucellus a large cell 

 becomes marked out, as in Angiosperms; this is the embryo-sac. The embryo-sac 

 becomes filled with an extensive tissue, the endosperm, and produces at its apical 

 end (towards the micropyle) a number of egg-cells. These vary in number from 

 2-15 in various Gymnosperms, but in any case they are all assembled together 

 beneath the micropyle. Associated with each egg-cell is a neck, recalling that 

 structure in the archegonium (or amphigonium) of Ferns (c/. p. 67). Fig. 315^ 

 shows the tip of a gymnospermic ovule in section, considerably enlarged. Note 

 the funnel-shaped micropyle (with germinating pollen-grains in it) and two large, 

 oval egg-cells in the endosperm below. The slight shading above the tips of the 

 two egg-cells indicates the necks. The contents of the egg-cells in this figure have 

 already given rise to several cells, as in the stage represented fertilization has just 

 occurred. The cells here shown in Ephedra (fig. 316 ^\ or in most other Gymno- 

 sperms a limited number of cells (often four) cut off at the base of ea(!h egg-cell, 

 develop into little embryos, of which, however, ultimately one only survives for each 



