THE DICOTYLEDONES 1643 



2. Thlaspideae. Cotyledons straight, radicle accumbent. Pods on 

 horizontal pedicels. Flowers white. Thlaspi, Iberis, Teesdalia, 

 Hiitchinsia. 



IV. Raphanoideae 



Pods indehiscent or with very short valves which cover a few of the 

 seeds only. 



1. hatideae. Pods indehiscent, one-seeded and one-celled. Isatis. 



2. Cakileae. Pods transversely two-jointed, the lower joint indehis- 



cent and seedless, or two-valved, and two or more seeded. The 

 upper joint one- or two-celled. Cramhe, Cakile. 



3. Raphaneae. Pods elongated, one-celled and many-seeded or 



indehiscent or jointed, the one-celled joints being indehiscent. 

 Raphamis. 



It should be explained that in the above classification the term "radicle 

 accumbent" implies that the embryo is so folded that the radicle lies against 

 the edges of the two cotyledons. "Radicle incumbent" means that the 

 radicle lies against the back of one of the cotyledons. (See also p. 1500.) 



It is impossible in the space at our disposal to do more than touch upon 

 some of the more interesting features of this large family. Mention has 

 already been made of the swollen storage organs which are developed by 

 some of the biennial genera such as the Turnip and the Swede. In such 

 plants the primary root and hypocotyl enlarge steadily during the first 

 year's growth, storing up reserves as they are made during that summer. 

 In the autumn most of the radical leaves die away and the root remains 

 in the soil. The following spring growth begins again, but this year only a 

 flowering shoot is formed. This may grow to a considerable size using up 

 the food reserves of the previous year to supply the seeds as they are formed. 

 It may be noted that the leaves produced on the inflorescence are small as 

 compared with the radical leaves of the previous year. In the Radish, a 

 similar swollen hypocotyl region develops early in the life of the plant and 

 the inflorescence is produced during the first year. Special methods of 

 vegetative propagation are found in certain species. Bulbils are formed in 

 the axils of the leaves of Dentaria bulbifera and on the leaves themselves 

 in Cardamine pratensis. 



The flowers are remarkably constant so far as the six stamens are con- 

 cerned. These are arranged in two whorls; the outer consisting of a pair of 

 lateral stamens with shorter filaments and an inner group of four stamens 

 with longer filaments. These latter may remain more or less united even 

 in the adult flower. This tetradynamous character of the flower was first 

 observed by John Ray, and recorded in his "Historia Plantarum" (1686- 

 1704) and was subsequently selected as a diagnostic character of one of his 

 classes. Thus the limits of the Cruciferae today differ but little from 

 Linnaeus' original description. 



The morphological interpretation of the flower is uncertain. The two 



