Gymnospermae Conclusion. 



Relation of Conifers to other Gymnosperm Series. 



Gymnosperms constitute a relatively small but very important central group 

 in the Botany of Land-Flora, as presenting the story of the evolution and establish- 

 ment of the seed-stage (Archispermae) in dominant land-plants. All are more or less 

 archaic relics, more nearly related to the horizon of the Fern, with traces of aquatic 

 archegonial mechanism ; the groups largely comprise monotypes of special organiza- 

 tion, as forms now relegated to inferior biological environment ; hence the majority 

 are remarkably xerophytic. Any systematic arrangement still remains wholly pro- 

 visional. Modern phyla and even some genera may go back with little change to 

 the Cretaceous. Of 7 distinct lines of development, 3 are known only in the 

 fossil state. 



Note, the word Gymnosperm is probably only a conventional expression cover- 

 ing the end-terms of widely different phyla, all at a comparable horizon of seed- 

 evolution, and running more or less parallel in the progression of gametophytic 

 stages. ' Affinity ' within these groups need not be pressed too far, since all 

 Angiosperms must have passed through comparable phases in attaining minimum 

 reduction in their sexual prothallia, with limiting terms of siphonogamy and post-sexual 

 nutrition of the embryo. 



The most distinctive feature of their organization is the anatomy of the meta- 

 xylem, with tracheides connected by bordered pits on the radial walls only ; from 

 this only the Gnetales diverge. 



I. Pteridosperms : very Fern-like in general organization, as underwood 

 vegetation, with frond-leaves and definite seed-stages. Fossil only from Palaeozoic 

 (Carboniferous), especially in calcite ' coal-balls ' : cf. Lyginodendron, Heterangium. 



II. Cordaitineae : Forest-tree types of Devonian and Carboniferous. Timber 

 much as Araucaria : flowers small, more in the manner of Pinus, in compound 

 inflorescences. Leaves large ; seeds in strobili, often large. Fossil only, cf. Pitys 

 Withami (Nat. Hist. Mus.) and Craigleith (1830), 47 ft. trunk, \\ ft. at top. 



III. Ginkgoales (1/1); Forest-tree types of Tertiary to Mesozoic : only 

 survivor Ginkgo biloba, with Conifer wood, plum-like seed of Taxoid, andZoi'dogamy; 

 elementary pollen-tube system, pollenic chamber, and ' tent-pole ' mechanism. 



IV. Cyeadaceae (9/80); Plants of underwood or hill-slopes, with mostly 

 monaxial Tree-fern or Palm-habit, to 60 ft. ; tropical and sub-tropical ; Frond-leaves 

 bipinnate (Bowenia), usually once pinnate (Cycas), large, 2-6 ft. long. Staminate 

 flower (2 ft. in Ceralozamid) of spirally arranged stamens (to 500), with possibly (to 

 750) hundreds of pollen-sacs, and up to 30,000 pollen-grains in a pollen-sac (Dioon 

 Encephalarios) : Anemophilous. Ovulate flowers often immense, 30 lb. (Dioon), and 

 2-3 ft. (Microcycas). Ovules borne on definite Carpels, several (Cycas), or 2 only. 

 Seeds may be as large as eggs (Dioon). Zoi'dogamic : microgamete of Dioon, 300 fx 

 diam., 5 coils of ciliated band, and visible to naked eye. 



V. Cycadeoideae ; Mesozoic plants of dwarf Cycad-habit (Bennettites), to Palm- 

 habit (Williamsonia) ; cf. Portland ' Fossil Birds' nests ' (Cycadeoided). and Wyoming 

 beds ; mostly silicified. Large floral-shoots borne singly in leaf-axils, with perianth, 

 large frondose bipinnate stamens, and ovulate cone for gynoecium : no apparent 

 ' carpels ' ; probably insect-pollinated. 



VI. Coniferae (40/350) ; Forest-trees of modern epoch; siphonogamic, and 

 anemophilous, with tendency to reduced ' needle ' or scale-foliage ; Pinoid cones, and 

 Taxoid arillate seeds. Pinus, Juniperus, Taxus, single species of three limiting cases, 

 alone indigenous. 



VII. Gnetales (3/45) ; Isolated relics of a very distinct series approaching 

 Angiosperms in some respects. Ephedra, a switch-plant, with no photosynthetic 

 leaves. Gnetum, a tropical-forest Liana-form, with broad net-veined leaves, and 

 inflorescences of small flowers, possibly insect-pollinated. Welwitschia extreme 

 desert-xerophyte, of rainless SW. Africa ; abbreviated woody trunk, 3 ft., with 2 

 immense foliage- leaves only, growing by basal meristem, and splitting. Inflorescence 

 panicled, ovulate cones (2 in.), with winged seeds : Staminate flower with perianth 

 (2 + 2), staminal-tube of 6 stamens, each 3 pollen-sacs, investing relic of sterile ovule, 

 with drop-mt^hanism adapted for insect-pollination. Definite relic of hermaphrodite 

 flower in minimum terms. 



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