A Synopsis of Plant Phyla 49 



collateral librovascular bundles are arranged concentrically in the 

 stem, and these increase its thickness by the development of their 

 cambium ; sporophylls in dioecious strobili. 



Family 9. Ginkgoaceae. Represented today by a single species 

 of Ginkgo^ a large Chinese and Japanese tree, but in the Tertiary 

 there were many species of this genus, and of other now wholly 

 extinct genera. (Pf. II, i, 108.) 



PPhylum XIII. GNETALES? The Joint-Firs. 



Chlorophyll-green terrestrial plants, shrubby in size and struc- 

 ture, with a branched or simple stem, undivided leaves, monoe- 

 cious sporophylls, and naked seeds. They are related to the Cy- 

 cads, and possibly should be included in that phylum. 



Class 32. GNETINEAE. With the characters of the phylum. 

 Three genera, little if at all related, compose this phylum, if in- 

 deed it be a phylum. They are usually referred to a common 

 family, Gnetaccac, with no good reason. The species of Ephedra 

 (about 20) are low evergreen shrubs, bearing opposite, reduced 

 leaves, and axillary clusters of simple, diclinous flowers. Tuinboa 

 (i species) is a genus of thick-stemmed woody plants, with two 

 long strap-shaped, opposite leaves, and bearing their simple flow- 

 ers in very regular, scaly cones. Gnetwn contains about fifteen 

 species of shrubs, bearing opposite, large, elliptical leaves, and 

 loose terminal scaleless cones. (Pf. II, i, 116.) 



Phylum XIV. STROBILOPHYTA. The Conifers. 



Chlorophyll-green terrestrial, woody plants, usually trees of 

 large size, in which the alternation of generations is obscured by 

 the reduction of the gametophyte to a condition of dependence 

 upon the long-lived, leafy-stemmed sporophyte. Spores of two 

 kinds (heterosporous), borne on sporophylls which occur in stro- 

 bili, the microspores set free (as "pollen"), the megospores re- 

 tained in their sporangia, where they develop gametophytes and 

 archegones. After fecundation of the egg by non-motile sperm- 

 atozoids (male nuclei) the embryo sporophyte, surrounded by the 



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