1640 A TEXTBOOK OF THEORETICAL BOTANY 



Cardamine pratensis (Milkmaids); Eroph'la verna (Vernal Whitlow Grass); 

 Thlapsi arvense (Penny Cress) and many others. 



The plants are generally herbaceous, rarely woody, and many are 

 annuals with a life cycle of only a few weeks. The leaves are alternate and 

 are normally beset with simple or branched hairs, the forms of which have 

 been employed in the systematic arrangement of the genera. The plants 

 may form storage organs, especially in biennials such as the Turnip or 

 Swede. 



The inflorescence is generally racemose and often a corymb. Bracts 

 or bracteoles are so rare that their absence is regarded as a family character. 



The flowers (Fig. 1 503) are hermaphrodite and actinomorphic, occasion- 

 ally somewhat zygomorphic; polypetalous and hypogynous, with the parts 

 arranged either in twos or fours. 



) 



Fig. 1503. — Cruciferae. Floral dia£;ram. 



The calyx is polysepalous and consists of four sepals which are arranged 

 in two whorls, the lateral, inner sepals being frequently pouched at the base. 



The corolla is polypetalous and cruciform; composed usually of one 

 whorl of four petals which are often differentiated into a narrow claw and a 

 broad, expanded limb. 



The androecium is composed of six hypogynous stamens which are 

 arranged in two whorls, the inner being composed of the four longer stamens 

 while the outer whorl consists of two short lateral ones (Fig. 1504). Nec- 

 taries are developed as small green glands at the base of the two short 

 stamens. Here the nectar accumulates as well as in the pouches formed by 

 the lateral sepals. 



The gynoecium is bicarpellary and syncarpous. The ovary is superior 

 and bilocular as a result of the development of a false septum which arises 

 from the parietal placentas. The ovules are generally numerous, anatropous 

 or campylotropous. The stigmas are generally commissural. 



The fruit is either a siliqua or silicula or a lomentum and this feature 

 is often used as a basis of classification. (See also below, p. 1642.) 



The seed is almost devoid of endosperm and the testa is often mucila- 



