CXXXIX.— THE COMMON YELLOW MELILOT. 
Melilotus altissima Thuillier. 
C OMING to the members of the Tribe Trifoliece in which the uppermost stamen 
is not united to the other nine, which, so far as British plants are concerned, 
comprise the genera Trigonella, Medicago, Melilotus, and Trifolium, the Fenugreeks, 
Medicks, Melilots, and Clovers, we find them all to be herbaceous, with pinnately 
trefoil leaves having toothed margins, and flowers that secrete honey. They may be 
distinguished from one another by their inflorescences and pods. Trigonella has a 
short raceme and a curved dehiscent pod, longer than the calyx ; Medicago has a 
short raceme and a pod which is usually spirally colled ; Trifolium has its flowers in 
a head and a short pod ; and Melilotus has its flowers in a long raceme, with somewhat 
similar straight pods. Linnaeus, however, united Tournefort’s genus Melilotus with 
Trifolium, to which it is unquestionably very nearly related. 
Melilotus includes some twenty species, natives of the Warm and Temperate 
regions of the Old World, two or three of which may be indigenous in Britain. 
They are mostly annuals which are apt to form some wood in their stems during 
the first season and to survive into a second year, especially if browsed down during 
the first. The species occurring in this country include two with yellow blossoms 
and one with white ones. Of the former, M. altissima Thuillier, the common species, 
is the more robust ; has the deeper yellow flowers, with petals nearly equal in 
length ; and black, pointed, compressed, hairy pods ; whilst M. officinalis Lamarck 
has pale buff flowers, with wing and standard petals longer than the keel, and olive- 
brown, blunt, rounded, smooth pods. There has been a good deal of unfortunate 
confusion over the name of this latter, rarer species. 
It requires some little care to discriminate among leaves of three leaflets 
between those which are formed on the pinnate, and those formed on the palmate, 
type. In this genus it is fairly obvious, but in Medicago less s6, that the terminal 
leaflet has a longer foot-stalk or petiolule than the two lateral leaflets in the same leaf. 
This is an indication of their pinnate arrangement, abnormal extra leaflets arising 
lower down the main petiole than the normal lateral leaflets. In Trifolium, on the 
other hand, all three leaflets have equal stalks, and in “Four-leaved Clover” the 
fourth leaflet generally arises palmately at the same point as the normal three. 
The compound leaves of the Leguminosce afford many admirable examples of 
the so-called “ sleep ” movements of fully-formed organs. One general result of 
these Is that the leaflets, which are generally horizontal, or at right angles to the 
incidence of light, during the day, become vertical at night ; and Darwin suggested 
a reason for this by showing experimentally that leaves which are fixed in a horizontal 
plane suffer more from the cold of frost radiated from the ground beneath them. 
The mechanism by which the leaflets fall into the vertical is the flow of the watery 
contents of the thin-walled cells of the pulvinus, or swelling at the base of each leaflet, 
