PART III. THE CLASSIFICATION OF PLANTS. 



The development of the seed-coats varies widely. In the 

 Cycadaceaa the testa consists of two layers, an outer fleshy and 

 succulent, and an inner hard and woody, so that the seed bears a 

 superficial resemblance to a fruit such as a plum : in those Coni- 

 feraa in which the seeds are produced in a cone-fruit, the testa is 

 hard and tough ; but in those in which the seed is exposed from 

 the first, the testa is either fleshy (e.g. Ginkgo, Cephalotaxus), 

 being developed after the manner of that in the Cyeadaceae, or it 

 is hard, and is invested by a succulent aril (e.g. Taxus, Podo- 

 carpus). In those Coniferse with woody cones (e.g. Abietinece, 

 Araucarinese, most Cupressineae) the seed is usually winged, either 

 by means of a membranous outgrowth of the testa, or (Abietinere) 

 by the adhesion to the seed of a thin strip of tissue, split off from 

 the surface of the placental scale. Among the Gnetaceae, the 

 testa is hard and woody in Ephedra and Gnetum ; in Welwitschia 

 the seed is enclosed by the expanded perianth, which acts as a 

 wing. 



Classification of the Gymnospermce. 



The class contains the following three orders : 



1. CYCADACE^E: the trunk is generally unbranched : the leaves 

 are large and branched : no vessels in the secondary wood. 



2. CONIFEE^:: trunk much branched: leaves many, small, and 

 unbranched : no vessels in the secondary wood. 



3. GrNETACK-ffi: habit various: flowers have a rudimentary 

 perianth : there are vessels ia the secondary wood. 



Order 1. Cycadaceae. The Cycadaceae are plants which, in many respects, 

 show affinity with the Ferns, while, on the other Land, they resemble the 

 Palms in external appearance. The stern is tubercular or cylindrical. The 

 vegetative leaves are of two kinds ; scaly leaves, brown and dry, closely 

 covering the surface of the stem ; foliage-leaves, pinnate, of a leathery consis- 

 tency, produced annually or at a longer interval, forming a crown at the top 

 of the stem ; the foliage-leaves are generally developed expanded, but in Cycas 

 the piiinse are circinate in vernation, as is also the phyllopodium in Stangeria 

 and Zamia. 



The dioecious flowers are produced, either singly or several together, at the 

 apex of the stem ; they are cones (except Cycas). The development of the 

 cones does not arrest the growth in length of the stem : hence the stem may 

 be regarded as a sympodium, its growing -point being maintained by either 

 dichotomous or lateral branching (pp. 33, 35). The macrosporophylls of Cycas 

 do not constitute a true flower, since they are not borne, as in the other genera, 

 on a special axis, but simply take the place of a whorl of foliage-leaves. The 

 cones consist of an elongated axis, bearing numerous spirally-arranged scaly 

 sporophylls, which vary in number from 30 to 600. The microsporoph.ylls bear. 



