720 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



are produced in close proximity to the apex of the plant, and sometimes (as in the 

 female cone of Cycas) are actually terminal in position. The scales (stamens) of 

 the male cones are usually boat- or shield-shaped, and bear very numerous pollen- 

 sacs on their under surfaces, often aggregated into little groups or sori. The female 

 cones are generally more massive than the male, and their scales (carpels) are shield- 

 like or scale-like in form. In Cycas revoluta (cf. fig. 208 '', p. 74) the carpels more 

 nearly resemble the foliage - leaves, and the ovules are borne in the position of 

 leaflets. In other genera the number of ovules is restricted to two. Pollination is 

 accomplished by the wind, and the ovule as it ripens develops a hard shell enveloped 

 in a fleshy coat. The seed thus exhibits the superficial characters of a drupe {cf. 

 p. 428). 



Cycads are restricted to the warmer regions of the globe, and are especially 

 characteristic of the Floras of Australia {Macrozamia, Bowenia, Cycas) and Central 

 America {Zamia, Ceratozamia, Dioon). There are nearly 80 species, belonging to 

 9 genera, and they have mostly a somewhat restricted distribution. Fossil remains, 

 from the Cretaceous onwards, are abundant, and show that in former times the 

 Cycads foi'med a much more important constituent of the vegetation than at the 

 present day. 



A living collection of these interesting plants is cultivated in the Palm-house in 

 Kew Gardens; it is exceedingly rich in forms, all the genera, and a large number of 

 the species being represented. 



Class II.— CONIFERS. 

 Alliance XXVII. 



Families: AraucariacecB, Abietinece, TaxodieoB, Cupressinece, Taxacece. 



The Coniferae, which include the various Pines, Firs, Junipers, Cypresses, and 

 Yews, have characteristically branched stems. The leaves are usually linear and 

 needle-like or scaly, rarely possessing an expanded lamina. The flowers are 

 unisexual, and occasionally the sexes are on difiierent individuals. In by far the 

 larger number of Conifers the flowers are cone-like, i.e. aggregates of scales set 

 upon a central axis and bearing respectively ovules and pollen-sacs. The stems of 

 Conifers thicken up in the manner characteristic of Dicotyledons, but the secondary 

 wood is composed entirely of tracheides (fibre-shaped elements), with peculiar 

 bordered pits {cf. vol. i. figs. 10 '•'■*' p. 45); vessels are absent from it. In a great 

 number of forms resin-ducts are present. 



The families above given fall into two groups. The first of these includes the 

 AraucariaceaB, Abietineae, Taxodieee, and Cupressinese, and is characterized by the 

 female flowers being cone-like. In the Taxacese, on the other hand, the female 

 flowers are rarely in cones. 



Araucariacece. — This group is familiar to everyone in the widely cultivated 

 Chili Pine or " Monkey-puzzle " {Araucaria imbricata). The cones are made up 

 of scales spirally arranged, and the ovules are solitary on the scales of the female 



