CHAPTER XIV. THE SPERMAPHYTA. 365 



— the multiform adaptations of stems, leaves and roots, for exam- 

 ple, to a variety of uses and changes of form to correspond with 

 changed functions — is especially remarkable. While dichoto- 

 mous branching is common in other groups of plants, in this it 

 is the rare exception ; roots, stems and leaves, if they branch at 

 all, branch monopodially ; the stems and roots do not grow by 

 the division of a single apical cell, as is the case in all Pterido- 

 phyta, except the Lycopodines, but by a group of cells ; and 

 the fibro-vascular bundles of the stems and leaves are different 

 in kind, being usually of the collateral variety. 



By far the larger proportion of all Seed-plants are chloro- 

 phyll-bearing. Only a few have developed parasitic or sapro- 

 phytic habits. 



The Series is subdivided into two Classes, the Gymnosperm.e 

 or Seed-plants without ovaries, and the Angiosperm;e, or Seed- 

 plants with ovaries. 



THE GYMNOSPERM^. 



The plants of this class are, without exception, woody-stem- 

 med, terrestrial and chlorophyll-bearing forms, most of them 

 attaining a considerable size, and some of them forming the 

 largest of our forest trees. In the structure of their stems they 

 show affinities with the highest forms of the Series, the Dicotyle- 

 dons, since they possess a pith, medullary rays and a cambium 

 zone; but their tissues are less complex, true wood-cells, and 

 ducts being largely replaced by an intermediate tissue, the discig- 

 erous tracheids. In many other points they show themselves 

 decidedly inferior to the rest of the Spermaphyta, and, in some 

 important respects, closely allied to the Pteridophyta. The 

 flowers, as a rule, are of very simple structure, consisting of 

 leaves much less modified from the ordinary form than in most 

 other flowering plants ; they are never showy or nectar-bearing ; 

 the stamens and pistils are never found together in the same 

 flower, but all the plants of the Class are either monoecious or 

 dioecious ; as implied in the word, gymnospermce, the ovules are 

 not enclosed in an ovary, but are borne on the base of an open 

 carpel, or, more rarely, naked, on the end of a branch, and the 

 cotyledons of the embryo are arranged in whorls, sometimes of 

 two, but often of four, six, or some higher number. 



