THE DICOTYLEDOXES 1645 



dehiscent, one-seeded pods are formed in Isatis tinctoria (Woad) which 

 still grows wild along the cliffs bounding the River Severn. 



In some genera the pod may be laterally compressed, and as a result 

 the septum becomes very broad, as is seen in Lunaria rediviva (Honesty). 

 Alternatively the pod may be flattened from back to front, when the septum 

 remains very narrow. This is well seen in Capsella hursa-pastoris (Shep- 

 herd's Purse). 



Mention may be made of the genus Morisia, which contains one species, 

 a native of Corsica and Sardinia. In this annual herb the peduncle bends 

 down after flowering, and buries the closed pod in the ground close to its 

 roots. Another interesting case of a specialized distribution mechanism is 

 exhibited by Anastatica hierochuntica, the Rose of Jericho, a native of the 

 eastern Mediterranean. While the seeds are ripening in the dry season, the 

 leaves fall off and the branches fold inwards, reducing the plant to a ball 

 enclosing the fruits. The whole plant, which is an annual, now becomes 

 free from the soil and is blown about until it reaches a wet spot or 

 the rainy season begins, when the branches uncurl and the seeds are 

 liberated. 



All the Cruciferae are entomophilous and most of them are homo- 

 gamous. The inflorescence which may begin as a corymb becomes, by 

 elongation, a raceme and renders the flowers fairly conspicuous. However 

 the flowers of many species are not sufficiently noticeable to ensure regular 

 insect visits and we find that all the Cruciferae are capable of automatic 

 self-pollination. 



The calyx is apparently designed not only to protect the developing 

 flower but later holds the petals together in a tube, at the bottom of which 

 lie the nectaries. Despite the general similarity in structure of the floral 

 parts there are considerable differences in the number and position of the 

 nectaries, not only in relation to the stamens and the stigma, but also in the 

 mode of storing and concealing the nectar. (See p. 1244.) 



Velenovsky, who has made a detailed study of over 170 species, found 

 that nectaries were invariably present. From this analysis Velenovsky 

 suggests that it would be possible to classify the Cruciferae on the basis of 

 the position and form of the nectaries. Since the nectaries are presumably 

 essential in pollination they must obviously be important in the evolution 

 of the flower, and therefore of the family. 



ROSALES 



The Rosales are Archichlamydeae in which the flowers are mostly 

 actinomorphic and cyclic or spirocyclic. Both sepals and petals may be 

 present or one or both may be missing. When present they are free and 

 imbricate or valvate in the bud. The stamens may be the same as, or a 

 multiple of, the number of the petals; they may be perigynous or epigynous 

 or less commonly hypogynous. The ovary similarly may be either superior 



