AN ENCYCLOPADIA 
OF HORTICULTURE. 77 
Pergularia - continued. 
soft, downy, 4in, long. China, &c., 1784. ae . 4 Š 
B. R. 412). e 2 * Re ery 
P. ang N (bloody. juiced). enish-yellow ; es 
many-flowered, shorter than the fenton dale e ai 5 
late, quite glabrous. Sierra Leone, 1822. Plant trailing, full of 
blood- coloured juice. (B. M. 2532.) 
PERI. Greek for around; e.g., as in Perianth. 
PERIANTH. The outer, or accessory, organs in 
the flower, i.e., the sepals and petals, which protect the 
essential organs of reproduction, or the true flower, in 
NG. 84. PETALOID PERIANTH, as seen in Lilium concolor 
3 vulehellum. 
botanical language, i.e., the stamens and pistil. In most 
flowers, the perianth is double, consisting of an outer 
circle of green sepals, and an inner circle of coloured 
— — 
r TS 
Fie. 85. SINGLE PERIANTH, as seen in Anemone sylvestris. 
petals (as in Abutilon, Fig. 83). In the Liliacew, and 
other plants, the perianth, though double, consists of parts 
very much alike, and all petaloid (Lilium concolor, Fig. 
| spreading to other trees. ps 
Perianth—continued. 
84); while in others—e.g., Juncus, &e.—all the parts are 
sepaloid. Often one of the circles is wanting, and the 
missing circle is usually the petals, though (as in. 
Anemone, Fig. 85) those present may appear petaloid. 
Often such single perianths are sepaloid (Mercurialis). 
In a good many plants (Willows, Arum), there is no 
trace of perianth. In many plants, the bracts are modi- 
fied to simulate part of a perianth (sepaloid bracts of 
Dianthus, and petaloid bracts of Cornus suecica). 
„ Included under Hyacinthus (which 
see). 
PERICALLIS. 
see). 
PERICALYMNA. Included under Leptospermum. 
PERICARP. The rind or shell of all fruits. 
PERICLADIUM. The sheathing base of a leaf 
when it expands and surrounds the supporting branch; 
the dilated, sheathing base of some petioles. 
PERICLINIUM. The involucre of the flower-heads 
in Composite. 
PERICYCLA. A synonym of Licuala (which see), 
PERIDERM, PERIDERMIS. The outer cellular 
layer of bark, below the epidermis. 
PERIDERMIUM from peri, around, and derma, 
skin). A group of Fungi, including only a few forms, 
parasitic on Conifere. Those of most importance are 
P. elatinum (also called Acidiwm elatinum), which 
gives rise to swellings on the branches of the Silver 
Fir (Abies pectinata), and P. Pini, with its variety 
P. acicolum, on the Scotch Fir (Pinus sylvestris) and 
the Austrian Fir (P. austriaca), in pleasure grounds, as 
well as in forests. The genus belongs to the group of 
“red rusts,” and the Fungi in it form a mycelium in 
the tissues of the leaves and branches of the host-plants. 
On the surface of the diseased parts there appear, after a 
time, cylindrical, laterally flattened, or conical outgrowths, 
called peridia, Win. to zin. high, and win. to tin. broad; 
the larger forms being on the branches, and the smaller 
on the needles. These outgrowths are formed of a thin 
layer of cells, which tears irregularly at the tip, and 
sets free numerous small, round, orange-coloured spores, 
to reproduce the plant. 
P. (Zicidium) elatinum is not very frequent; but where 
it is present the tree sometimes bears a large number 
of swellings on the branches, often near the base of one 
or more small branches, or supports what are known as 
“witch-besoms”’ on the larger branches. Both kinds of 
growth are the work of the Fungus; and the difference 
is due chiefly to age. The swellings vary from the size 
of a Hazel nut to that of a closed fist; the bark is the 
part most enlarged. The mycelium grows in the bark 
and the pith-rays and pith, and often causes separation 
of the bark from the wood, and the death of the wood 
in patches. In most cases, it does not kill the branch 
entirely; but the mycelium is perennial, and the growth 
on the branch continues to increase year after year. 
When branches grow from the surface, they often branch 
very freely, but remain stunted; and this is repeated 
year by year, the “witch-besoms” being thus formed. 
The leaves on the diseased shoots are short and stunted, 
and are usually covered with peridia. Though not 
usually, or only very slowly, dangerous to the life of 
the tree, the growths are very objectionable, as they 
greatly spoil its appearance. The only effectual remedy 
is cutting off the diseased branches as soon as the 
swellings appear, in order to prevent the disease from 
Included under Senecio (which 
P. Pini grows in branches of Firs, and almost always 
