CRUCIFER^E, OR TURNIP TRIBE. 



369 



edges of which are not entirely folded in; and the ovules arise, 

 therefore, from a placenta formed by the 

 thickened edges of each leaf, so that there 

 are really four separate placentae, as is 

 indicated by the four different directions in 

 which the ovules lie (Fig. 140, C). But 

 the contiguous placentae of the two carpels 

 unite together, and project towards the 

 middle of the ovarium ; and in this instance 

 the opposite ones meet each other, so as 

 to form a complete partition. In many 

 Cruciferous plants, on the other hand, they 

 do not meet ; so that the ovary is one-celled, 

 and as the ovules are attached to its sides, 

 the placentae are said to be parietal. The 



li * w< A fl V """ ., . ., . .. 



the valves ; 6, the torm of the fruit ditters in the different 



FIG. 140. A, ripe fruit 



marks of the places to which explained in the Liimaean Classification 



the seeds are attached; C, Actn\ j.* ,1 



dissepiment with seeds at- ( . 48d), sometimes, as in the present 



tached; D, section of seed. instance) a snorfc pO( J 



:; and some- 

 times a long pod or siliqua, as in the Turnip and Cabbage, 

 Stock, and Wall-flower. This distinction is not employed, 

 however, to subdivide the order in the Natural system ; since it 

 is not found to bring together the plants that have really the 

 nearest alliance : and Botanists found their classification of the 

 genera (which, on account of their great number, need to be 

 associated in groups) upon certain minute distinctions presented 

 by the embryo. Throughout the order, however, the structure 

 of the seed is different from that which has been elsewhere seen; 

 for it is entirely destitute of albumen ; and the embryo is doubled 

 upon itself. (Fig. 140, D). 



531. All the plants of this order are herbaceous, and most of 

 them are annual. The flowers are usually yellow or white, less 

 commonly purple. It is remarkable that, whilst the characters 

 of the order are so constant, those of the individual are liable to 

 such great variation. This is evident in the species which are 

 cultivated for the beauty of their blossoms, such as the Stock 



