THALAMIFLOR^ 93 



Mustard (Brassica alha), Whitlow Grass {Draha 

 verna), Awl Wort (Stibularia aqiiatica), Pennycress 

 {Thlaspi arvense), Sea Rocket {Cakile maritima). 



These nine types are representatives of the sub- 

 divisions into which the order can be divided 

 according to the character of the cotyledons or seed- 

 leaves, and the character of the fruit, whether opening 

 or not. 



In the Siliquosae or Crucifers in which the pods 

 are longer by three to four times than broad, there 

 are two groups. The pods open longitudinally 

 from top to bottom, and are flat or swollen, not 

 compressed, at right-angles to the septum. The 

 pods are short in Nasturtium, however, and the top 

 in Brassica does not open. In Draha, in the second 

 group, the pod is a siliqua, longer than broad. 



Amongst those divisions of the first group with 

 seeds in one row (or in two in Arahis dind Nasturtium), 

 and in which the radicle is accumbent — that is, lying 

 against the edges of the cotyledons in the embryo, 

 which is curved — there is the Arabis tribe. The 

 Cuckoo flower has been selected as a type of this 

 tribe. It has a small stigma, which is terminal and 

 simple, and flat pods with elastic valves. Other 

 members of this tribe are the Seastocks, Wallflower, 

 Water Cress and allied species, the Winter Cresses, 

 the Wall Rockets, the Bitter Cresses, and Coral- 

 root. 



In the other tribe Treacle Mustard has been 

 selected as a type. The seeds in the Hedge Mustard 



