Explanation 
of plate. 
Botanical 
description. 
156 
XXVIII. Trefoil. 
Medicago lupulina, L. 
Fig. A. The flower bearing stems, natural size. 
1, The flower, side-view. 
2, The same, with calyx removed. 
., o& The same, with calyx and standard removed. 
%. The keel, and sexual organs. 
5. The sexual organs. 
,» 6. The pistil. 
7. The pod and persistent calyx. 
,, 8. The seed, from the broad side. 
, 9. The seed, shewing the hilum, 
Botanical description. The tap-root produces few branches, and descends vertically to a depth 
of about one foot. The stem branches, which build up the plant, spring from the crown of the root 
(basal branches), and extend horizontally for some distance before bending up into the air; this mode 
of growth gives the plant a very diffuse and spreading character. 
The stems are partly horizontal and partly ascending, branched, somewhat angular, covered with 
adpressed hairs, and from four inches to two feet in length. The Jeaves are alternate, compound, and 
trifoliate. The radical leaves have longer petioles than the cauline. The Jeaflets are obovate, wedge- 
shaped (cuneate) at the base, Loothed (denticulate) at the apex and petiolate; the partial petiole of the medium 
leaflet is longest. The stipules are lanceolate, often toothed (Fig. A.). 
The inflorescence is, at first, a spherical head which later becomes somewhat elongated and spike- 
like. The peduncle is axillary and much longer than the leaf. The flowers are very small — at most 
3mm. long. The calyx (fig. 4) is half as long as the corolla, but longer than it is in the variety parvi- 
flora, Doll.; the tube is pubescent, and deeply split superiorly; the teeth are five in number, and 
lanceolate. The standard (figs. 1 and 2) has a broad claw which, at the base, is slightly coherent both 
with the wings and the keel; the limb is broad, curved upwards, and completely envelopes the other 
petals. The simgs are small, and have narrow claws; the keel is somewhat similar in structure. 
Wings and keel together cover the lower part of the sexual organs, while the anthers and stigma 
lie exposed beneath the standard, Nine of the stamen filaments unite together to form a narrow trough, 
embracing the lower edge (dorsal suture) of the ovary (fig. 5); the free stamen is only half as long as 
the others (figs. 5 to 5), 
Compared with the other parts of the flower, the pistil (figs. 3 and 6) is relatively large; the 
ovary is compressed and its lower surface hairy, the style short and curved upwards, the stigma capitate 
and placed at a short distance above the anthers. 
Little or nothing is known concerning the relations between these flowers and insects. Miiller 
noticed bees, flies, and butterflies visiting the flowers. Darwin observed, further, that plants covered 
with a net to prevent the visits of insects were much Jess fertile than others to which the insects 
had free access, 
The variety parviflora is probably merely a female form of the plant, and, in that case, trefoil is an 
example of gynodioicism. 
The fruit (fig. 7) is a pod, which is black, one - seeded, compressed, reniform and seated in the 
persistent calyx; the apex is curved; the surface is glabrous — except in the var. Wildenowii which has 
glandular hairs — and has projecting ribs which are concentric and reticulate. . 
The seed (figs, 8 and 9) is yellowish-brown, shining, compressed at the sides, and elliptical. The 
hilum is round, and lies on one of the narrow faces; immediately above it. the tip of the radicle forms 
a slight projection. 
