212 VEGETABLE SUBSTANCES. 



aware of the production of this mephitic gas, of the 

 noxious effects of which they are sometimes made 

 fatally sensible. Under particular states of the wea- 

 ther, which are known to the overseers from expe- 

 rience and observation, the men do not then go to 

 work until a fire-grate has been let down in one of the 

 ventilation pits, as deep as the rooms or galleries in 

 which the operations are to be carried on. If the fire 

 in the grate will not burn, of course their labours are 

 suspended, until, by the play of the atmospheric cur- 

 rent between pits at different elevations, the supera- 

 bundant carbonic acid gas is removed. 



The principal legumes cultivated in Britain are the 

 pea, the bean, and the kidney-bean; which, according 

 to the analyses that have been made, contain quan- 

 tities of nutritive matter, diminishing in the order in 

 which they have been enumerated, and all of them 

 much less than any of the cerealia. 



Peas contains fifty-seven and a half per cent of nu- 

 tritive matter, a proportion of which is saccharine. 

 Beans have very nearly as much nutriment, but it is 

 not entirely composed of the same principles. No 

 saccharine matter ready formed is found in this vege- 

 table, which is considered a coarse though nutritive 

 esculent. Kidney-beans do not contain more than 

 nine per cent of nutritive matter. 



THE PEA Pisum is a climbing plant, furnished 

 with tendrils at the terminations of the compound 

 leaves ; and none of the species, not even the dwarf 

 kind, can sustain their stems in an upright position, 

 without either interlacing with each other, or clinging 

 to some extraneous support. 



The varieties of this genus are very many. Bota- 

 nists enumerate several species, which they regard as 

 being distinct. The chief of these are the common or 

 cultivated pea (pisum snlivum^ the sea-pea (pisum 

 maritimum}, the Cape-Horn pea (pisum 



