132 SEEDS. 



(67) Black Mustard Seeds. 



The seeds of Brassica nigra, Koch (N.O. Cruciferse). 



In the seed-coats the following layers can be distinguished : 



(1) An epidermis (am) composed of large thin-walled cells 

 containing mucilage. 



(2) A single layer of large parenchymatous cells, the walls of 

 which are not collenchymatous, as those of white mustard seeds 

 are. These cells are generally collapsed, and lie closely pressed 

 on to the next layer of cells. In the powdered drug they are not 

 sasy to see. 



(3) A single layer of dark brown sclerenchymatous cells (sc) 

 which, in transverse section, exhibit the very characteristic 

 thickening (s'c ( ) shown in the illustration. Some of these cells at 

 regular intervals ate longer than the others, and thus produce the 

 pitted appearance of the seed as well as the peculiar, polygonal 

 network seen in the surface view of the seed-coats. 



(4) A thin membranous layer (cm) consisting of large, poly- 

 gonal, flattened cells, containing a brownish amorphous sub- 

 stance. This layer is closely applied to the sclerenchymatous 

 layer, and in the powder generally remains firmly adherent to 

 it, producing, in part, the characteristic colour of the seed. 



(5) Within the seed-coat is an aleurone layer (ap) consisting 

 of rather thick-walled, polygonal cells, containing aleurone 

 grains. Next to this row of cells is a layer composed of several 

 rows of collapsed parenchymatous cells, the cavities of which 

 are only indistinotly visible as faint lines. 



The cotyledons (co) are covered by a transparent epidermis, con- 

 sisting of polygonal cells. They contain small irregular aleurone 

 grains, in each of which numerous minute globoids can be 

 detected. 



The powdered seeds contain very numerous fragments of the 

 delicate tissue of the cotyledons and radicle ; in glycerin these 

 exhibit the characteristic aleurone grains, which may also be 

 found scattered over the preparation. Examined in chloral 

 hydrate globules of fixed oil are very conspicuous Fragments 

 of the seed-coat are easily recognised by their brown colour ; 

 they usually present their surface view and exhibit the poly- 

 gonal network above alluded to. Colourless, transparent frag- 

 ments of the epidermis may also be found as well as portions of 

 the aleurone layer. 



The diagnostic characters of powdered mustard seeds are : 



(a) The dark, yellowish-brown sclerenchymatous layer. 



(b) The polygonal network exhibited by the upper surface 

 of that layer. 



(c) The small aleurone grains, each with numerous minute 

 globoids. 



(d) The mucilaginous cells of the epidermis. 



