a 
ROELLA. 
ROELLA. A genus of ornamental Cape-of 
Good-Hope plants, of the bellflower family. Six 
or seven species, chiefly blue-flowered summer- 
bloomers of about a foot in height, some annual 
and others perennial, some herbaceous and others 
ligneous, have been introduced to the gardens of 
Britain. 
ROHAN. An artificial pace of specially- 
trained riding-horses in Egypt and Turkey. It 
resembles the amble in easy effect, but differs 
essentially from it in character, and gives the 
horse an awkward, straddling, broken-backed ap- 
pearance. It is produced by so loading the pas- 
terns of the hind legs with metallic discs as to 
prevent the fetlock-joints from bending, and to 
cause their office to be peformed by other por- 
tions of the limb; and it, in consequence, ren- 
ders the foot-fall comparatively soft and the seat 
of the rider comparatively free from concussion ; 
and, when it is fairly formed, the metallic discs 
are removed. 
ROLLER,—scientifically Ooracias. A genus of 
birds, of the crow division of passerine. The com- 
mon roller, C. garrula, is an occasional visitor of 
the shores of Britain. It is about the size of the 
jay, and has a total length of 13 inches. Its 
general plumage is sea-green and various shades 
of blue; its back and scapulars are fawn-coloured ; 
the tip of its wing is pure blue; and several 
parts of its body are tinged with verditer, brown, 
and black. It is a very wild bird, though socia- 
ble enough with its fellows; it is noisy, and 
builds in the hollows of trees, and migrates in 
winter; and it feeds on worms, slugs, insects, 
small frogs, and berries. 
ROLLER. An implement for compressing, 
smoothing, pulverizing, or otherwise finishing- 
off cultivated land, whether in grass or in tillage, 
| in preparation for sowing or subsequent to sow- 
| ing, in a newly sown state or after the appear- 
| ance of the nascent crop. Both the forms and 
| the uses of the roller, in fact, are exceedingly 
diversified; and some of the most useful imple- 
ments of the roller class differ so very widely 
| from all the old and common rollers, and at the 
same time from one another, as to take to them- 
selves peculiar names, such as drill-roller, seam- 
| presser, and clod-crusher. 
All the old or early rollers were simply cylin- 
ders, and may be supposed to have been employ- 
ed only for breaking down the cloddy and lumpy 
portions of tilled stiff soil preparatory to sow- 
| ing, and for compressing and smoothing and con- 
solidating light and driftable lands immediately 
| subsequent to sowing; and such rollers are still 
oO? 
| confined to the same principal uses, with the ad- 
dition of the smoothing and compressing of grass 
| lands. They are thought by some writers to have 
| come into existence coevally with the plough, 
or with the rudest stirrer of the soil, or at least 
to have appeared immediately after it,—and cer- 
tainly they occur in countries where agricultural 
processes are in a very rude and almost nascent 
Ek wt hn i a a cn bens 
“ROLLER. 
state ; yet they are assigned by other writers to 
an epoch later than the harrow, and even than 
the grubber,—or to one in which the pressure of 
increasing population drove farmers by necessity 
to the cultivation of stubborn and adhesive soils, 
and compelled them to invent mechanical means 
for breaking hard clay clods. The cylindrical 
roller, at all events, is known to have been till 
recent times the only implement of its class; 
and though this might seem to a superficial 
thinker to have been quite simple and unique 
and incapable of variety, it really received, in the 
course of time, a great diversity of size and 
weight and construction, and was made first en- 
tirely of wood, then of stone with a wooden. 
frame, and then in various ways of iron, and 
came at last to be formed of two or three or more 
parts, revolving either on the same axle or on in- 
dependent axles. 
The common rollers, or land-rollers, of the pre- 
sent day comprise all the varieties which have 
ever been used, except the most rude and ancient. 
The wooden ones are either pieces of heavy solid 
timber, of the full diameter of a large tree, or 
hollow cylinders, variously constructed, and of | 
comparatively large diameter; and though they 
make little impression on any but very light 
soils, they are highly serviceable for levelling po- 
tato or turnip drills, for compressing the earth 
about newly sown seeds, and for some other and 
analogous light purposes. Some are spiked with 
iron or encircled with large metallic rings, to as- 
sist in crushing clods; many or most have simple 
contrivances, generally a weight-containing box 
on the upper part of the frame, for temporarily 
increasing their weight and pressure; and all are 
mounted with a skeleton cart-like frame, ter- 
minating in shafts for one or two horses, or with 
attachments for four or even six oxen, according 
to their respective size and weight. The com- 
mon solid wooden rollers of England are usually 
made of oak or ash, and generally vary from 5 to 
74 feet in length, from 16 to 20 inches in diameter, 
and from 10 to 15 cwt. in weight, but occasion- 
ally are 9 feet in length, from 20 to 30 inches in 
diameter, and so heavy as to require to be drawn 
by 4 horses or 6 oxen. A very common roller in 
Scotland 20 or 30 years ago, and one most easily 
and cheaply procured, had a wooden axle, with 
two or three rows of spokes placed in it accord- 
ing to its length, and felloes placed on the ex- 
tremity of the spokes in the manner of a cart- 
wheel, and planks or boards of wood fastened on 
the felloes all round; and a closely similar roller, 
of still more facile construction, is now occa- 
sionally made in England, with three broad 
wheels of the required diameter,—two of them 
placed at the ends and the other in the middle 
of the required length,—and with an iron axle 
passing through the whole, and adjusting them 
to their positions, and with strong, narrow, 
bevelled planks nailed firmly lengthwise round 
all the exterior. 
Some hollow wooden rollers — 
