718 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



allotted. In the Pteridophytes, fertile "cones" are frequently met with. They are 

 assemblages of leaves bearing sporangia, and with the shedding of the spores 

 accomplish their function. But in the Phanerogams it is not so. The stamens, 

 having shed their pollen-gi-ains (microspores), truly are done with. But the carpels 

 which bear the ovules persist in situ until the ripening of the seed. And in the 

 vast majority of Phanerogams, structures accessory to the stamens and carpels have 

 become associated with the flower. These, forming the perianth, promote the 

 transfer of pollen by attracting insects to the flowers in the innumerable ways 

 already fully indicated in this volume. A minority of species depend on wind, and 

 are destitute of attractive perianths. It is worthy of passing notice that wind- 

 pollinated plants, though relatively few in species, are well represented in number 

 of individuals in the various Floras of the globe. It is sufficient to instance the 

 Conifers, Grasses and Sedges, Palms, Amentaceae, and Urticaceee. 



The phylum Phanerogamia is divided into two sub-phyla, Gymnospermse and 

 Angiospermse, which differ technically in that in the former the ovules are exposed 

 on scales and receive the pollen-grains direct into the micropyle, whilst in the latter 

 the ovules are borne in closed chambers, the ovaries, and the pollen is received on a 

 special organ, the stigma 



Sub-phylum A.— GYMNOSPERM.äl. 



The pollen is received direct upon the nucellus of the ovule, whence the pollen- 

 tube penetrates to the egg-cell. The embryo-sac (macrospore) is filled with the 

 endosperm (prothallium) which bears archegonia sunk in its substance at that end 

 which is directed towards the micropyle. In almost all cases the archegonia possess 

 neck- and canal-cells in addition to the egg. 



The phenomena accompanying fertilization and seed-production in the Gymno- 

 spermse having been described at pp. 418 and 437, brief statements of the general 

 external characters alone are given below. 



The Gymnospermse are divided into 3 Classes: Cycadales, Coniferse, Gnetales. 



Class I.— CYCADALES, Cycads. 



Alliance XXVI. 



Family: CycadacecB. 



In habit the Cycads generally resemble the Tree-Ferns and Palms. They possess 

 for the most part unbranched columnar stems terminating in a crown of large pin- 

 nate leaves. The surface of the stem is scarred with the bases of the fallen leaves, 

 and recalls in appearance that of the fossil Lepidodendrons (cf. p. 71G). In height 

 Cycads do not exceed about 12 metres, and usually they do not attain even these 

 dimensions. The flowers take the form of cones of closely aggregated scales, which 

 vary in number from 30 to 600. The cones are respectively male and female, and 



