The Natural System of Botany. 177 



ould immediately know that this species at least would be 

 t only harmless, but the very best kind of vegetable for you 

 to consume; a salad which might be eaten with the utmost 

 confidence. 



To return to the Shepherd's Purse; the sepals are four, and 

 t he petals four, arranged in the form which gives rise to the 

 appellation of Cruciferae, or Cross-bearers. The pistil is green, 

 wedge-shaped, and bears the short style and flat stigma on its 

 summit. If the ovary be cut open, it will be found to contain 

 two cells, in each of which are a number of ovules, hanging by 

 slender thread-like stalks, and originating, not from one pillar, 

 like central placenta, but from a kind of partition which 

 extends quite across the ovary to its sides. This shows the 

 reason why in this order the ovary is often one-celled, and also 

 explains the peculiar mode of dehiscence of the seed vessel. 

 The fruit becomes a triangular, wedge-like body, heart-shaped 

 at the summit, and is composed of three pieces, two of which, 

 the valves, separate from the third, the dissepiment, and it is to 

 the edges of this last piece that the seeds are united. The 

 mode in which this curious seed vessel is formed will serve as 

 another illustration of the theory which refers all parts of 

 plants to different developments of the leaf. In this case, each 

 valve is considered to be a carpellary leaf, the two edges of 

 which are not entirely folded in, and the ovules arise, therefore, 

 from a placenta formed by the thickened edge of each leaf, so 

 that there are really four separate placentae, and the ovules lie 

 in four different directions. But the contiguous placentae of the 

 two carpels unite together, and project towards the middle of 

 the ovary, and in this instance the opposite ones meet toge- 

 ther and form a complete partition. In many other Cruciferae, 

 they do not meet, so that the ovary is one-celled, and the pla- 

 centa parietal. This whole examination must of course be con- 

 ducted by the aid of the microscope, and may be somewhat 

 obscure and difficult, but the student will have learned the 

 means of recognising with certainty the characters of this 

 great tribe of plants, so widely diffused over the globe, all of 

 which are quite harmless when eaten, and some of which are 

 most excellent and salutary. 

 The fruit of many Cruciferae differs from that which we 



