PRINCIPAL GROUPS OF PLANTS. 113 



the leaves form a crown at the summit of the stem or trunk. 

 An important character of some of the Cycads is the production 

 of multiciliate sperms, as in the ferns, Equisetum and Isoetes. 

 (2) The Ginkgonaceae (to which belongs the Ginkgo or Maidenhair 

 Tree, which is extensively cultivated in China and Japan and is 

 found wild in China. It is very widely cultivated in this country, 

 owing to its ornamental foliage ; the staminate tree is preferable, 

 as the seeds of the pistillate tree have a very offensive odor. The 

 triangular shaped leaves occur in fascicles and the seeds are 

 berry-like. (3) The Coniferae is by far the most important group 

 and consists of two families, the Taxacese and the Pinaceae. To 

 the Taxaceae belongs Taxus, or yew, a low tree bearing flat, linear 

 leaves and a seed which is exposed and surrounded by the scarlet, 

 fleshy, aril-like disk or scale. 



To the Pinacese belong most of our important Gymnosperms. 



Pinus (Pine) is the most important genus (Figs. 67, 73, and 

 74). It is characterized by having needle-like leaves arranged 

 2 to 5 in a fascicle. The cone of the pine is usually woody, and 

 upon becoming dry splits open so as to release the winged seeds. 

 Perhaps the most valuable member of this genus is the white pine 

 (Fig. 67) which is found throughout the northern half of the 

 United States east of the Mississippi River. Its timber is light 

 brown or reddish, soft and fine-grained, but not very strong. 

 It is used extensively in rough building construction. 



Pinus palustris, or long-leaved pine, is one of the most valuable 

 members of this group. It is the chief source of the terebinthinous 

 products of this country, and its wood contributes no small part 

 to the lumber industry. The long-leaved pine is tall, straight, has 

 a thin-scaled bark and a very hard, resinous wood. The stem 

 separates near the summit into several diverging branches, giving 

 the tree a flattened top. The leaves are in threes, rarely in fours, 

 from 10 to 15 inches long, and the cones are 6 to 10 inches long, 

 the scales being armed with short recurved spines. Other pines 

 yielding turpentine are Pinus Tada, loblolly pine ; Pinus hetero- 

 phylla, Cuban or swamp pine ; Pinus echinnata, short-leaved yellow 

 pine. 



Tsuga canadensis (Hemlock) is a common tree of eastern 

 North America (Fig. 73). It attains a large size, and the delicate 

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