BRIEF REVIEW OP THE SYSTEM OF LIFE. 



435 



483. 



..-■yv-. 



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/ 



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481. 



482. 



wood of the modern tree has a very large pith abounding in starch, surrounded hy one or 



more rings of wood, each the result of several years' growth. 



The ordinary "Evergreen" trees, as the Pine, Spruce, Arbor Vitse, Yew, belong to 



the second and higher subdivision, the Conifers^ so-called because the flowers and fruit 



ordinarily have the form of cones. In the 



Pine family the fruit is a cone ; but not so in 



the Yews. The Salisbw'ia, or Ginkgo, a tree 



with short and broad, somewhat fanlike leaves, 



is generally referred to the Yew family, though 



having some relations to the Cycads. 



The woody fiber of the Conifers is marked 



with circular disks as in Figs. 481, 482 ; fossil 



woods of the order may thus be distinguished, 

 and genera may often be 

 distingTiished by their ar- 

 rangement. 



Another aberrant 

 group, the Gnetacece, in- 

 cludes the genera, Gnetum, 

 Ephedra, and Welwitschia ; 

 and the last, of which only 

 one species exists, and that 

 in Africa, approaches the 

 Angiosperms, in its flower, 

 "the staminal flower con- 

 taining a rudimentary 

 ovule." But it has the 



broad strap-like leaves of the ancient Cordaites, and also, as the Fig. 483 shows, the 



winged form of fruit characteristic of the Carboniferous Cardiocarpus. 



2. Angiosperms. — The higher Exogens, or the Angiosperms, have the seeds covered ; 



the flowers perfect, the wood consisting largely of vascular tissue as well as woody fibers. 



Examples are the Maple, Elm, Apple, Chestnut, Rose. 



Circular disks on the 

 woody fibers of 

 C(jnifer6. 



Fig. 483, Welwitschia mirabilis, showing trans- 

 verse section of fruit, with the outline of the 

 fruit finished in dotted lines. 



2. Endogens. 



The Endogens are represented by the Palm, Rattan, Smilax, Grasses, Orchids. A 

 section of a woody stem, as that of a Rattan (a species of Calamus) or Smilax, shows the 

 ends of woody fibers and ducts. The leaves are parallel-veined instead of net-veined, 

 and not toothed, and the parts of the flower are commonly in threes. 



Cryptogams, or Flowerless Plants. 

 1. The Higher Cryptogams, or Acrogens. 



The Acrogens consist of cellular tissue with more or less of fibro-vascular tissue, and 

 are capable of upward growth, whence the name from dicpov, top, and yeuvdoo, grow. 



The lowest species have special interest in the geological history of plants. They are 

 called Bhizocarps (root-fruited) from the position of the fruit at the base of the stem, or 

 at the root. The figures represent, half the natural size, species of three of the very few 

 forms now existing. They show the position of the nuts, and the unlikeness of the species 

 in habit to most Cryptogams. Fig. 486, of Salvinia natans, represents a section of the 

 plant showing only one of the pairs of leaves in the floating plant. 



