370 NATURAL THEOLOGY. 



to the light and air by the bursting of the stem or 

 the expansion of the petals; after which they have, 

 in many cases, by the very form of the flower du- 

 ring its blow, the light and warmth reflected upon 

 them from the concave side of the cup. What is 

 called also the sleep of plants is the leaves or petals 

 disposing themselves in such a manner as to shel- 

 ter the young stems, buds, or fruit. Tiiey turn up, 

 or they fall down, according as this purpose ren- 

 ders either change of position requisite. In the 

 growth of corn, whenever the plant begins to shoot, 

 the two upper leaves of the stalk join together, 

 embrace the ear, and protect it till the pulp has ac- 

 quired a certain degree of consistency. In some 

 water-plants the flowering and fecundation are 

 carried on within the stem, which afterwards 

 opens to let loose the impregnated seed.* The 

 pea, or papilionaceous tribe, inclose the parts of 

 fructification within a beautiful folding of the inter- 

 nal blossom, sometimes called, from its shape, the 

 boat or keel — itself also protected under a pent- 

 house formed by the external petals. This struc- 

 ture is very artificial ; and what adds to the value 

 of it, though it may diminish the curiosity, very 

 general. It has also this further advantage, (and 

 it is an advantage strictly mechanical,) that all the 

 blossoms turn their hacks to the wind whenever 

 the gale blows strong enough to endanger the deli- 

 cate parts upon which the seed depends. I have 

 observed this a hundred times in a field of peas in 



♦Philos. Transact, part ii. 1796, p. 502. 



