SWEET PEA, 37 
Of these petals the upper, called the standard, enfolds all 
the rest in bud; while the two at the side, named 
the wings, enclose the inner two, which are more or less 
united by their edges to form the keel. From the fancied 
. , Fig. 42, Wing Fig. 43. Keel 
oe 41, eas, of SE UIBAL Pod of Sweet Pea 
Sweet Pea flower. Hawer, flower. 
resemblance to a butterfly, such flowers as this are called 
papilionaceous.* On removing all the petals, observe the 
10 stamens, also fastened to the base of the calyx-tube and 
forming a sheath to the ovary: 9 of them have their filaments 
united into a tube, while the one opposite the standard is 
free (= diadelphous).| The pistil consists of an elongated 
ovary, tapering into a style bent nearly at right angles, and 
ending in a minute stigma. On cutting the ovary transversely 
you will find it is formed of a single carpel, having a single 
row of ovules arranged along the ventral suture. If you have 
@ pod to examine, you will see that it opens, when ripe, by 
both its sutures, and this form of fruit is called a legume.? 
The seeds are very easily examined, but the type is still better 
made out, on account of its size, in the bean (which sce, p. 39). 
On account of their extreme irregularity, bright colours, 
fragrance, and minute stigmas, we are justified in inferring 
that the flowers of this plant, and, indeed, all of the type, are 
fitted for fertilisation by insects. At the same time, a very 
large number of plants of the pea-tribe, and this species 
among them, seem to be quite fertile even when all insects are 
excluded from visiting the flowers. 
(a.) Garden Pea (Piswm sativwm).—Note the perfectly glabrous 
character of this plant, the two or three pairs of leaflets developed, and 
the relatively immense stipules, evidently intended to perform the leaf- 
work. And, correlated with this leaf-development, note the absence of 
the wings on the stems and petioles which are so characteristic of the 
Sweet Pea. The flowers and fruit differ only in slight details from the 
preceding. ) 
(6.) Broom (Cytisus scoparius) differs (inter alia) in having its 
stamens monadelphous, a character common to a large number of papilio- 
naceous plants. Whin (Ulex ewropeus) has its branches, and, in many 
* Lat. papilio, a butterfly. 
| Gr. dis, twice ; adelphos, a brother. 
} Lat. legwmen, pulse. 
