GROUP IV. GYMNOSPERM.E. 419 



GROUP IV. GYMNOSPERM^. 



The plants of this class are all perennial trees and shrubs, for 

 the most part evergreen : they are classified into the three natural 

 orders, Cycadaceae, Coniferse, and Gnetaceae. 



THE SPOROPHYTE. 



General Morphology of the Vegetative Organs. The 



body is distinctly differentiated into stem, leaf, and root. 



The Stem grows above ground, usually erect, but climbs in 

 several species of Gnetum : it is woody, and is generally branched 

 monopodially : the symmetry of the main stem is radial, whilst 

 that of the branches is frequently bilateral, either isobilateral (e.g. 

 Thuja, phylloclades of Phyllocladus) or dorsiventral (e.g. species of 

 Abies, Taxus, and many other Coniferse in which the branches are 

 horizontal). The branches in many Coniferse (e.g. Pinus, Larix, 

 Cedrus, Ginkgo) are dimorphous, being either long shoots or dwarf- 

 shoots (see p. 23) : in the other forms the dwarf-shoots bear foliage- 

 leaves and fall off, sooner or later, with the leaves which they 

 bear : in Pinus the dwarf-shoots alone bear foliage-leaves, whilst 

 in the other genera the long shoots bear foliage-leaves as well. 



The Leaves are either foliage- leaves or scale-leaves. The foliage- 

 leaves are either small and numerous, as in the Coniferse ; or large 

 and few, as in the Cycadacese, and as in Welwitschia where there 

 are only two foliage -leaves : they are branched only in the 

 Cycadacese : they are sessile in the Coniferse and in Welwitschia : 

 their growth is basal : their form varies considerably, one of the 

 most peculiar forms being that characteristic of certain Conifers 

 i Abietinese) where the leaf is needle-like (acicular) and either 

 flattened or prismatic and angular. The leaves fall annually 

 in only a few forms (e.g. Larix, Ginkgo) ; in the others the leaves 

 persist for two to ten years, or, as in Welwitschia, throughout the 

 life of the plant. 



Scale-leaves, destitute of chlorophyll, occur in nearly all the 

 Cycadacete, in most Conifers (absent in most Cupressinese) and in 

 Ephedra (Gnetacese). 



The Primary Root always persists as a tap-root. 



General Histology. The Stem. The growing-point of the 

 stern, whilst generally conforming to the structure characteristic of 

 Phanerogams (see p. 102), does not present a clearly-marked differ- 



