42 On the different Species, 8pc. of the Genus Brassica. 



reserved for food. Among the varieties of the Brassica campes- 

 tris which, by reason of its large seeds, appears to be eminently 

 oleiferous, the Colsa is the most productive, and has the thin- 

 nest root ; for the produce of oil, the Ruta-baga and common 

 Napo-brassica are much less useful. In the Brassica Rapa f 

 the Navette with a thin root is cultivated for its oily seeds, 

 whilst the Turnip, or Brassica Rapa depressa, is used for food. 

 In the Brassica Napus, the Navette with a thin root is culti- 

 vated for its oil, and the Navet for the sake of its root. Lastly, 

 in the Raphanus sativus, the same circumstance again appears; 

 the thin roots constantly belong to the many seeded varieties, 

 whilst the thick fleshy roots are employed for culinary pur- 

 poses only. A similar law may be observed in other crucifer- 

 ous plants. The Cochlearia Armoracia, (Horse-radish), which 

 has a very large thick root, rarely brings any seeds to perfec- 

 tion, whilst every other species of Cochlearia produces them 

 freely ; this observation may be useful to guide cultivators in 

 the choice of the varieties proper to try as oleiferous plants. 

 If taken in a more extensive sense, it may serve to throw some 

 light on the laws of vegetation in general, for we know it is 

 not confined to cruciferous plants alone ; and I should be 

 tempted to elucidate this idea, were it not a digression in a 

 memoir of this nature. There is no doubt that much re- 

 mains to be done to make the history of Cabbages and Rad- 

 ishes clear and satisfactory. For this purpose it will be 

 necessary to assemble the different varieties cultivated in 

 those countries where I have had few correspondents on 

 the subject. The nomenclature of the divers European 

 languages ought to be ascertained and compared with pre- 

 cision ; cross fecundation tried in order to obtain the ex- 



