. The theory of evolution in the light of facts. female embryo embryo ova are found in the embryo seed. The first classes of this series are: Cycadinee(Sago or Fern Palms), Ginkgoinse (a still living speciesis Ginkgo biloba), Coniferso (Fir Trees), Gnetinae (asmall exotic group). 5. Angiospermse or plants with covered seeds.—The flowers often contain both male and female organsat the same time ; more rarely these are borne inseparate flowers or even separate plants. The pollengrains are only two-celled ; fertilization can only occurwhen the pollen grains, on germination on the st
. The theory of evolution in the light of facts. female embryo embryo ova are found in the embryo seed. The first classes of this series are: Cycadinee(Sago or Fern Palms), Ginkgoinse (a still living speciesis Ginkgo biloba), Coniferso (Fir Trees), Gnetinae (asmall exotic group). 5. Angiospermse or plants with covered seeds.—The flowers often contain both male and female organsat the same time ; more rarely these are borne inseparate flowers or even separate plants. The pollengrains are only two-celled ; fertilization can only occurwhen the pollen grains, on germination on the stigmaticsurface, send a tube down through the entire stalk tillit reaches the entirely enclosed embryo ova in the seedvessel. Each embryo only contains one ovum. The chief divisions are : Monocotyles and series 4 and 5 are distinguished from the otherthree as flowering or seed-bearing plants. A floweris produced at the terminal point of a shoot and con-sists exclusively of reproductive organs. The leaf 126 THE THEORY OF EVOLUTION. Fig. 27.—a, Ripe pollen grain ofanAngiosperm ; b, germinat-ing pollen grain; g, generatinggerm; v, vegetative germ. formation is transformed either into fruit or pollen-bearing leaves, or into protective or attractive means in connection with the fertiliza-tion. Seed plants they arecalled because it is throughthe seed that the formation ofnew individuals, separatedfrom the mother plants, iseffected. A seed is a multi-cellular body, which, when itleaves the mother plant, is already differentiated (agrain of wheat, an apple pip). It has been possible to establishthe existence of an alternation ofgenerations in the Gymnospermsand Angiosperms, but certainly of avery debased kind. A series of in-dications point to the pollen grains,and the so-called embryo sac in thebud germ, as being spores/ sincethey, in the first place, without fer-tilization, form a sort of prothallus(second individual ?) in which firstarises the fertilizing cell prope
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