728 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



tattered and broken. Welwitschia, once established, does not increase much in 

 length but continually in thickness. From the edge of its disc, in the leaf-axils, 

 arise branches which bear cones (cf. fig. 411). The male cones are small, and in the 

 axils of their scales occur flowers consisting of 6 stamens united together into a 

 sheath and surrounding a central structure which resembles an ovary, and contains 

 a single ovule, which is, however, so far as is known, always abortive. This ovary- 

 like structure is provided with a trumpet-like " stigma ", and the occurrence of this 

 remarkable structure in the male flowers points to the fact that the ancestors of 

 this plant possessed hermaphrodite flowers. The fertile female flowers occur in the 

 axils of the scales of other much larger cones, which become bright red in colour. 

 Each flower consists of a perianth containing an ovule with 2 integuments, but 

 although the inner of these integuments is very long, there is no stigma-like 

 structure as in the male flower, and the pollen-grain reaches the nucellus. The 

 developmental history of the ovule and embryo is exceedingly peculiar — as it is also 

 in Gnetum — but we cannot enter into these matters here. 



Sub-phylum B.— ANGIOSPERMJl. 



Ovules contained in closed ovaries. Pollen received on a specialized portion of 

 the carpel known as the stigma, and fertilization achieved by means of pollen-tubes 

 which penetrate hence to the ovule. 



Angiosperms fall naturally into two classes, Monocotyledones and Dicotyledones. 



Class I.— MONOCOTYLEDONES. 



Includes Flowering Plants whose flowers typically have their parts arranged in 

 whorls of three, embryos with one cotyledon, vascular bundles scattered through the 

 stem and not thickened by a cambium, leaves usually parallel-veined. 



The Monocotyledones may be divided into 6 alliances :—Liliiflor88, Scitaminese, 

 Gynandrse, Fluviales, Spadiciflorse, and Glumiflora. 



Alliance XXIX. — LiliiflorsB. 



Families: Juncacece, LiliacecB, AmaryllidacecB, Iridacece, Bioscoreaceoe, Brome- 

 liacece, Gommelynacece, Pontederiacece. 



In this alliance the flowers are actinomorphic, and their parts arranged in whorls 

 of three, i.e. two whorls constituting the perianth, two (or one) whorls of stamens, 

 and a whorl of three carpels united together. This condition may be briefly repre- 

 sented by the following formula:— P 3 + 3, A 3 + 3, G <3). in which P, A, and G stand 

 for perianth, androecium, and gynaeceum respectively. The bracket inclosing the 

 number of carpels indicates that they are united (syncarpous). The ovary is 

 3-celled, and may be either superior or inferior; the seeds contain endosperm. 



The LiliiflorsB are for the most part herbs with perennial imderground bulbs, 

 corms, and rhizomes. In relatively few cases is a permanent above-ground system 



