756 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



has a perianth 66 cm. long and 28 cm. broad. In the Asaraceas there are some- 

 times three small teeth alternating with the three perianth-segments, and tliese 

 are looked upon as reduced inner perianth-segments. The stamens of Aristolo- 

 chiaceae are adnate to the stylar column (see p. 292, fig. 284 ^'-). The Aristolochiacese 

 are distributed in all parts of the world. The majority of the species are found in 

 tropical and sub-tropical regions. The genus Asarum reaches furthest north. The 

 northern limit of the Asarabacca (Asarum Europceum) and its highest elevation 

 are the same as those of the Beech. Fossil remains are found in the strata of the 

 Mesozoic and Tertiary Periods. The number of extant species hitherto identified is 

 about 200. 



Alliance XLI. — Euphorbiales. 



Family : Eiiphorhiacem. 



Annual and perennial herbs, shrubs, and trees. Flowers in racemose or umbel- 

 late cymes; actinomorphic, hermaphrodite, pseudo-hermaphrodite, monoecious, and 

 dioecious. Floral-leaves differentiated into calyx and corolla. Calyx and corolla 

 3-12-merous. The corolla is often suppressed, and sometimes the calyx also is 

 wanting. In these cases the floral-leaves are replaced by bracts and involucral 

 leaves. The gy nseceum is superior, and is composed of 3-20 carpels, which are 

 arranged in whorls round a central column. The carpels are joined together to 

 form a multilocular pistil. In the inner angle of each loculus are 1-2 pendulous 

 ovules. The stamens vary in number from 1 to over 100. At the base of the 

 flower are some peculiar glands, which are looked upon as outgrowths of the 

 receptacle. They are either in the form of separate cellular structures, arranged 

 in a whorl, or else are coherent in the form of a cup. In the cases where these 

 structures do not occur they are replaced by similar glands, which are seated upon 

 the margin of the cup-shaped involucre. The fruit is a schizocarp or drupe ; 

 sometimes it is baccate. The embryo is imbedded in an abundant fleshy endosperm. 



It is difficult to describe the Euphorbiales in few words on account of their 

 extraordinary variety. Some of them contain watery juices; the majority are full 

 of latex. Several of the laticiferous species are poisonous. Many have green 

 foliage-leaves; whilst some are destitute of foliage-leaves, and assimilation is then 

 efifected by means of the green cortical tissue of switch-like or cactiform branches 

 and phylloclades. In many genera, especially in Eiiphorhia, the inflorescences 

 have the appearance of being single flowers. A large number of male flowers are 

 assembled together within a cup-like involucre, the free edge of which is furnished 

 with glands as though with petals. Each of these flowers consists, however, merely 

 of a bract and a stamen, and in the midst of them is a female flower, borne at the 

 end of a long stalk, and resembling a stalked ovary. In many species of the genera 

 Croton and Poinsettia the inconspicuous flowers are surrounded by bright-coloured 

 bracts and involucral leaves. In the majority of instances three carpels are devel- 

 oped, which are remarkable for their rotundity. They are laterally coherent, and 

 usually separate when mature, and become detached from the central column. The 



