THE DICOTYLEDONES 1897 



Many are cultivated in gardens, particularly those from the Mediter- 

 ranean region. Alkanria tinctoria yields Alkanet Root, while species of the 

 genus Cordia, many of which are trees, yield the valuable tropical American 

 timber known as Aloewood and Princewood. 



SOLAN ALES 



The Solanales are Metachlamydeae in which the plants are mainly herbs 

 or twiners, with alternate leaves. The flowers are usually actinomorphic 

 and pentamerous, and the ovary is superior, containing numerous or solitary 

 ovules grouped in one to five loculi. The seed is endospermic and the 

 embryo is generally curved. 



The order contains two important families: the Solanaceae, which we 

 shall consider in detail, and the Convolvulaceae. 



The Convolvulaceae were separated by Rendle into a distinct order, 

 the Convolvulales, which he also separated from the Tubiflorae. Engler 

 on the other hand included the family in the Tubiflorae. It is a family of 

 about 1,100 species divided among fifty genera. They are annual or 

 perennial herbs often growing by twining up other vegetation. The 

 flowers are often showy and are either borne singly in the axils of the leaves 

 or in axillary dichasia. The family is notable for having both latex and 

 bicollateral bundles. The flowers are hermaphrodite and actinomorphic; 

 and bracts often form an involucre. The sepals are often free but the petals 

 are joined to form a funnel-shaped, pentamerous corolla. There are five 

 stamens inserted towards the base of the corolla tube. The anthers have 

 two loculi. The ovary contains one to four loculi with either solitary or 

 paired ovules. The fruit is either a berry, a nut or a capsule. The cotyledons 

 are large and folded or crumpled in the seed, which is endospermic. 



Wettstein suggests that the Convolvulaceae may have had a distinct 

 origin from the other groups of the Tubiflorae and considers them as 

 allied phylogenetically to the Malvales or Geraniales. Hutchinson appears 

 to favour a close relationship of the Geraniales with the Convolvulaceae 

 and places the latter family among the Tubiflorae. 



A number of interesting plants belong to this family. Convolvulus 

 (Fig. 18 1 5) itself shows great variety of habit. Usually it is a twiner, but 

 in dry parts of Palestine and Arabia it becomes a spiny shrub. There are 

 three British species, two of which are usually placed in the related genus 

 Calystegia,i.e., C.sepium, the Common Bindweed, and C. soldanella, the Sea 

 Bindweed. The genus Ipomoea is very similar to Convolvulus, but often 

 develops a perennial tuberous rhizome. In some, e.g., I. batatas, the lateral 

 roots become fleshy and this plant is grown in the tropics as a vegetable 

 under the name of the Sweet Potato. The tubers are rich in both starch 

 and sugar. 



The genus Cuscuta (Fig. 181 6) includes a number of parasitic climbing 

 plants collectively termed Dodder. Many cause considerable damage to 

 the plants on which they live. C. trifolii on Clover and C. epithymum on 



