CHAPTER XVII 



THE GYMNOSPERMAE : CONIFERALES AND 

 TAXALES, THE PINES AND YEWS 



The Gymnospermae include the simpler members of the Spermatophyta 

 and form, as it were, a bridge between the Pteridophyta on the one hand, 

 and the Angiospermae on the other. They are more ancient than the Angio- 

 sperms and in their method of reproduction they show indications whereby 

 we can recognize the way in which the Angiospermic flower may have 

 evolved, though this does not imply that any living Gymnosperm can be 

 regarded as an ancestor of the Angiosperms. 



The group includes the Pines and Yews, together with a number of less 

 known groups, for example the Cycadales, the Ginkgoales and the Gnetales, 

 the latter having certain characters in common with the Angiospermae. 



In the Gymnosperms, as in the Angiosperms, the reproductive organs 

 are aggregated into flowers, but these diflFer considerably from those of the 

 higher Flowering Plants. In the Angiosperms the female reproductive organ 

 or ovule is enclosed in a special protecting structure, the carpel, which forms 

 a closed ovary. In the Gymnosperms the ovules are borne exposed on 

 sporophyllous scales. Hence the term Gymnospermae or " naked seeds " 

 has been given to this group. 



The most important order of the Gymnosperms is the Coniferales, which 

 includes Pines, Spruces, Firs, Larches, Cypresses and Araucarias. They are 

 mostlv evergreen trees, though a few, like the Larch, lose their leaves in winter, 

 while some, like the Juniper, seldom attain the size of trees. Most of the 

 Conifers grow in relatively dry, poor soils, and the leaves show modifications 

 which enable them to combat these arid conditions. Plants w^hich live in 

 dry habitats are termed xerophytes, and one of the characteristics of such 

 plants is that the leaves are usually small and so constructed as to expose a 

 reduced surface to the drying action of the atmosphere. This is true of the 

 majority of the Conifers, in which the leaves, or " needles " as they are 

 popularly called, are very narrow and resemble in appearance small green 

 shoots. 



In this respect the Conifers differ markedly from the Cycads in which the 

 leaves are ver>' large and are more like those of the Ferns. In fact in 

 the Gymnosperms we have two main structural types, the one exhibited by 

 the Conifers, with much branching and small leaves, the other typified by the 

 Cycads with few branches and large leaves. A marked difi'erence in the stem 

 anatomy exists between the tree-like Conifers and the shrub-like Cycads. 

 The wood in the first type is dense and massive and has been called 



22 657 



