CRUCIFEM 137 



occur in Tetrapterygium, Calepina, Boleum, and Zilla amongst 

 the Isatideae, and several other genera in this tribe show an 

 approach to the same arrangement by the cotyledons being 

 longitudinally concave, slightly folded or longitudinally plicate, 

 as in Myagrum, Schimpera, and Texiera. All the seven genera 

 of the Isatidese just mentioned have short one- to two-celled 

 fruits with as many seeds, thick and lignified pericarps, the 

 thicker parts of which become corky while the fruit is indehiscent. 

 As far as the fruit is concerned they seem reduced forms of 

 Cruciferse adapted for countries with a dry climate , or for dry, 

 rocky, or chalky places. They may also be allied to the Bras- 

 siceae, just as Crambe, Muricaria, Rapistrum, Enarthrocarpus, 

 Hemicrambe, Erucaria, Guiraoa, Fortuynia, Physorhynchus, 

 and Morisia amongst the Cakilinese, undoubtedly are. Rapha- 

 nus and Kaffenaldia amongst the Eaphanese also approximate 

 to Brassica in the form of the embryo, but differ in having 

 fruits which break up into lomenta or indehiscent pieces each 

 containing one seed. The cotyledons of Anchonium and 

 Sterigma, also belonging to the Raphaneae, have incum- 

 bent and flat or concave cotyledons, showing a tendency to 

 become conduplicate. The shape of seeds having condu- 

 plicate cotyledons varies considerably, but taking Brassica, 

 Diplotaxis, Eruca, Succovia, Crambe, and Raphanus as types, 

 the seeds are globose or ovoid. This may be seen by reference 

 to Brassica oleracea or B. nigra. The relation of the seed to 

 the peculiar form of the cotyledon has been already described 

 (ante, p. 43). 



Raphanus sativus (fig. 62) and R. maritimus agree in most 

 essential particulars with Brassica, except that the seeds are 

 generally larger, and enclosed singly in indehiscent seg- 

 ments of the pod. A rather differently shaped seed occurs in 

 Zilla myagroides. The fruit is globular, indehiscent, thick, 

 lignified, and surrounded with another thick, ' suberous ' or 

 corky layer the exocarp. Two oval and slightly com- 

 pressed or lenticular seeds occupy a central position, side by 

 side but in separate cells. The corky exocarp and woody 

 endocarp would indicate adaptation to a dry climate, and we 

 find that the four known species are natives of North Africa, 

 Arabia, and Persia. 



