434 



PART IV. CLASSIFICATION. 



A 



In spite of the fact that so many of the Coniferse are polyembryonic (see 

 p. 424), and that each ovule contains several archegonia, the ripe seed con- 

 tains only a single embryo, though occasionally two are found (e.g. 

 Ginkgo). The embryo has two, or more, cotyledons, which are usually 

 epigean. 



The order, which includes 34 genera and about 350 species, may be 

 naturally divided into the two sub-orders, Pinoideae and Taxoidese, based 

 upon the structure of the macrosporangiate flower ; each of these sub- 

 orders includes several families, the 

 chief of which are described below. 



Sub-order I. PINOIDEAE. The ma- 

 crosporangiate flowers are cones ; the 

 seed has a woody or leathery testa, 

 is enclosed between the macrosporo- 

 phylls or the placental scales, and 

 has no aril. 



Fam. 1. Abietlnece : monoecious ; 

 on its upper surface at the base, the 

 macrosporoph3'll bears a large pla- 

 cental scale on the upper surface of 

 which two inverted macrosporangia 

 are borne. The ripe seed has two 

 wings derived from tissue of the 

 placental scale ; the microsporophyll 

 bears two microsporangia ; micro- 

 spores usually have expansions of 

 the exine; all leaves arranged spir- 

 ally ; cotyledons, more than 2, com- 

 monly 5, sometimes as many as 15. 



The more important genera may 

 be distinguished as follows : 



A. No dwarf-shoots; placental 

 scales flat ; seed ripens in one year ; 

 stem bears whorled branches. 



1. Fruit-cones erect, fall- 

 ing to pieces when ripe ; 

 foliage-leaves flat, cylin- 

 drical at the base, and not 

 decurrent; placental scales 

 about the same length as 



the macrosporophylls . Abies. 



2. Fruit-cones pendent, 

 falling off entire ; foliage- 

 leaves with decurrent pro- 

 jecting base. 



Leaves 4-angular ; placental scales much longer than the 



macrosporophylls Plcea. 



B. Long and d \varf -shoots. 



FIG. 255. Abies pectinaia. A Carpel c, 

 seen from above (ventral surface), show- 

 ing s the placental scale, and sfc the two 

 ovules (mag.) B Mature cone (nat. size) ; 

 p axis ; c carpel ; s enlarged placental 

 scale. C Ripe placental scale (s) isolated, 

 seen from above; so, the two seeds, each 

 with a wing (/). (After Sachs.) 



