554 BOTANY. 



Race V. Kohl-Babi, in which the short and few-leaved stem becomes 

 thick, bullous, and edible. 



B. ca/mpestris, of the same regions as the preceding, has given rise to 

 the various kinds of Turnips. Colza and Rape also are probably vari- 

 eties ; the latter are extensively cultivated in Europe for their oily 

 seeds, from which useful oils are obtained by pressure. 



Maphanus aativus, the Radish, is a native of China. 



Nasturtium Armoraeia, the Horseradish of Europe, has long been 

 cultivated for its pungent roots, which are used as a condiment. Ac- 

 cording to Dr. Gray, the plant, for some unknown reason, does not pro- 

 duce seeds in this country. 



N. officinale. Water Cress of Europe, and now run wild in many parts 



S'lQS. 536-41.— Seeds op CBTjoirER^. 



^^ 



Bto. 536. Fi9. 537. 



Fio. 541. 

 Fig. 539. 



Fig. 53fi.- Seed of Erysimum. Magiiifled. 

 Fig. 537.-1.1 'ngitudinal eeclion of seed. Magnified. 



Fig. 538. — Cross-section of seed, showing incumbent cotyledons. Magnified. 

 Fig 539. —Longitudinal section of teed of Arabia. Magnified. 

 Fig. 540. — Cross-section of eeed oiArabis, accumbent cotyledons. Magnified. 

 Fig. 541.— Cross-section of seed of Barbarea, imperfectly accumbent cotyledons. 

 Magnified. 



of the United States, and many other rapidly growing foreign and na- 

 tive species, are used as salads. 



Brassica alba, White Mustard, and B. nigra, Black Mustard, both 

 natives of Europe, are grown for their seeds, which when ground con- 

 stitute the common condiment Mustard. It is also of considerable 

 value in medicine. 



Isatis tinctoria, B. tall- growing European bienniiil, was formerly ex- 

 tensively grown for the blue dye obtained from it. 



The most important ornamental plants of the older are the Wall- 

 flower {CheirantUus), Gilly Flower or Brompton Stock (MattHola), 

 Rocket {Hesperis), Candytuft (Iberis), Honesty (l.v,na/ria), Sweet Alys- 

 sum (Alyssum), etc., etc. 



Several of the species are troublesome weeds- e g.. Shepherd's Purse 

 {Onpsella), which has come to this country from the Old World ; Pepper- 

 grass {Lepidium), native and introduced ; False Flax (Vamdinu) from 

 Europe ; Charlock and Mustard {Brassica) from Europe. 



