PEAS AND BEANS. 249 



The contents are proteid granules and oil globules. 



Ghemistry. — Mustard contains ^^ per cent, fatty oil, 

 about 18 per cent, proteid, 19 per cent, mucilage, and 

 4 to 6 per cent, ash, a glycoside, sinigrin, and a ferment, 

 myrosin, whose interaction in the presence of water yields 

 the volatile oil of mustard (allyl sulphocyanate). 



PEAS AND BEANS. 



A knowledge of the structure of the seeds of the pea 

 and the bean is of great ser\^ice to the student of phar- 

 macognosy, as these two seeds enter so largely into the 

 manufacture of so many products. 



The pea is the seed of Pisum sativum, L. , a universally 

 cultivated plant. Nat. ord. Leguminosece. 



Histology. — On the outside of the pea there is a thin 

 epidermis which is palisade-like in structure, the cells 

 being about 10 to 15 microns in diameter and 50 to 60 

 microns long. The walls are irregularly thickened and 

 are not lignified. The lumens of the epidermal cells are 

 very irregular. They are almost occluded by the thick- 

 ening of the cell wall in the middle of the cells; below 

 the lumen widens out perceptibly. Beneath the epi- 

 dermis a row of thin-walled irregularly quadrate cells, 

 the hypodermis, is found. These cells are about 35 

 microns in diameter, and have a somewhat dumb-bell 

 form. The remainder of the seed is formed of paren- 

 chyma largely filled with starch and with aleurone grains. 

 Tissues about the hilum show a slight thickening of the 

 cell walls, forming a double layer of palisade cells, and 

 certain elongated elements resembling tracheids may 

 be found. 



The cells of the cotyledon epidermis are isodiametric, 

 contain aleurone grains, while the main body of the 

 cotyledons is made up of large parenchymatic cells, 



♦ Die wichtigsten vegctabilischcn Nahrungs und Gcnussmittel. 



