THE GYMNOSPERMAE : CONIFERALES AND TAXALES 659 



northern limit of tree growth and probably cover a larger land area than any 

 other group of plants. Their leaves are usually either linear and needle- 

 like or else form green scales closely appressed to the stem. They may be 

 either whorled or spiral in their arrangement on the shoots. A few, like the 

 Monkey Puzzle [Araucaria imbricata), have broad leaves, but share the same 

 hard, cuticularized texture characteristic of the needle leaves. This leathery 

 consistency of the leaves is associated with anatomical characters which 

 point to a need for the conserv ation of water. 



The arrangement of the genera of Coniferales has not reached stability. 

 A number of sub-orders are recognized, but their limits and the genera 

 assigned to them vary with different authors. The inclusion of the Yews 

 in the order is also uncertain, and we here adopt the view that they should 

 form a separate order, the Taxales. The leading characteristics of most of the 

 sub-orders are, however, fairly clear and are given below with the principal 

 genera assigned to them. 



Araucariineae. Broad-leaved trees with very large cones ; mostly in 

 Australasia and South America. The ovuliferous scales are mostly completely 

 fused to the sporophylls, the free end being sometimes called a ligule. The 

 male gametophyte has many prothallial cells and the female many archegonia, 

 which is usually looked upon as a primitive character. The chief genera are 

 Araucaria and Agathis. 



Podocarpineae. Small trees, mostly in the Southern Hemisphere. 

 There are no female cones, the female flowers being borne singly in the axils 

 of bracts and containing only one anatropous ovule, which surmounts a fleshy 

 pedestal composed of the fused tissues of its stalk and of the bract. The 

 chief genera are Podocarpus, Saxegothaea and Dacrydium. 



Abietineae. Large trees with narrow or needle-like leaves, often borne 

 on foliar spurs. In the female cone the bract is free from the ovuliferous scale, 

 which is usually considerably the larger of the two. Mostlv North Temperate 

 in distribution. The chief genera are Pimts, Picea, Larix, Abies and Cedrus. 



Taxodineae. Large trees with narrow or spine-like leaves. In the 

 female cone the bract is almost completely united to the ovuliferous scale, 

 only the double end showing the composite nature of the combined structure. 

 The chief genera are Taxodium, Sequoia, Sciadopitys and Cryptomeria. 



Cupressineae. Trees varying from ver\' large size to mere shrubs. 

 Leaves usually small, often closely appressed to the branches and even fused 

 to the latter and to each other. Female cones small, the scales simple, 

 somewhat fleshy and only the upper ones fertile, larger than the others and 

 each bearing a number of erect ovules. Fertile scales sometimes fused together 

 at maturity. The chief genera are Cupressus, Thuja, Callitris and Juniperus. 



Pinus sylvestris (The Scots Pine) 



The genus Pi?nis includes about seventy-five species at present living. 

 Geologically its history does not go back beyond the Jurassic period, though 

 pollen grains which might be those of Pinus have been found in Triassic rocks. 



