AN ENCYCLOPEDIA OF HORTICULTURE. 



171 



Plusia continued. 



the silvery y. The hind wings have a broad, dark band 

 along the margin, and the basal space is pale grey. 

 The eggs are laid on the lower surface of the leaves. 

 The larvae are thickest at the twelfth segment, tapering 

 forwards. They are bright green, with bluish-green 

 dorsal line, bordered along each side with a white Ene; 

 and there are four more narrow white lines and a yellow 

 line on each side, near the spiracles or breathing pores. 

 There are a good many scattered, fine bristles on the 

 body. The larvae rest with the back arched, and move 

 by looping. They feed upon all kinds of herbs, including 



FIG. 208. PLUSIA GAMMA. 



Nettles and other weeds, as well as upon many low culti- 

 vated plants, such as Cabbages, Beets, Peas, Beans, &c. 

 The best methods of effectively lessening their numbers are 

 to destroy the larvae, either by hand-picking, or by sweep- 

 ing them, or beating them, off their food, and destroying 

 them at once; or ducks and hens may be turned in to 

 feed on them. Dusting the plants with soot or caustic 

 lime is also recommended, though not very safe for 

 delicate plants. Among the points to be specially attended 

 to is the removal of weeds from gardens and field crops 

 alike, as they afford shelter for the insects. 



PLUTHLLA CRTJCEFERARUM. A small moth, 

 known also as the Diamond-back or Turnip-moth, belong- 

 ing to the group of Tineina. It is excessively common 

 throughout Great Britain; and, despite its small size, 

 the ravages committed by the larvae in some years are 

 sufficient to force it on the notice of every observant 

 farmer and gardener. The wings are about fin. across. 

 They are narrow, with long fringes, and are of a greyish- 

 brown colour, with darker spots, the inner margin 

 bearing a long, pale ochreous streak, with three prolonga- 

 tions into the dark part. While at rest, the moths sit 

 in a very characteristic attitude, with the antennae held 

 straight forward, and nearly touching their support, and 

 the wings folded over the body, like the sloping sides 

 of a roof. The pale edges are thus in contact, and re- 

 semble a row of three diamond-shaped spots. The legs 

 are nearly hidden by the wings in the sitting insect. 

 The larvse are pale green in colour, with a darker head, 

 several black dots on the next segment, and two yellowish 

 spots on each of the next two segments. They have a 

 few bristly hairs on the body, which tapers a little 

 towards each end. They feed on the lower surface of 

 the leaves of Turnip, Cabbage, and other Cruet/era, 

 eating away the substance of the leaf between the veins. 

 Frequently, a dozen or more may be found on a leaf, 

 and, when very numerous, or while the plants are small, 

 the crop is apt to suffer severely. When full-fed, the 

 larvse spin slight cocoons in the hollows between the 

 leaf-veins on the lower surface, or on the soil, among 

 rubbish, and change into pale brown pupae, marked with 

 black lines on the back and wing-cases. The moths 

 emerge in from two to three weeks. There are two chief 

 broods in the year, the moths appearing in May and 

 August, and the larvae about a month or six weeks later. 



Remedies. These are very difficult of application, since 

 the larvse live protected by the leaves from the direct 

 application of insecticides, while their numbers and small 



Plutella Crnciferarnm continued. 

 size render hand-picking slow, and unlikely to be suc- 

 cessful, except on a small scale. The removal and de- 

 struction of leaves, with numerous larvae and pupae on 

 them, and also of surface rubbish in autumn, lessens the 

 risk to future crops. Brushing below the plants with 

 branches of Firs, or of other twiggy shrubs or trees, has 

 been recommended as likely to remove a number of the 

 larvae. Whatever favours rapid growth in the plants, 

 e.g., manures and watering the plants in dry weather, 

 will be of service; and gas lime and soot, thrown below 

 the plants, might assist in keeping away the moths during 

 the time of egg-laying, and in reducing the injury to 

 the leaves. 



FNEUMONANTHE. Included under Gentiana. 



POA (from poa, an ancient Greek name for grass or 



fodder). Meadow Grass. ORD. Graminece. A large genus 



(about eighty species) of hardy, sometimes dwarf annual, 



sometimes taller and perennial, grasses, broadly dispersed, 



but mostly found in North temperate regions. Inflorescence 



either in spreading or close panicles, the spikelete, for 



the most part, several-flowered and awnless ; outer glumes 



unequal, and generally keeled; upper pales shorter and 



narrower, with inflexed, membranous margins. Few of the 



species are grown in gardens, being mostly of agricul- 



tural value. Eight are British plants. The following are 



probably as much worth growing as any. They are of 



very easy culture in ordinary garden soil. Propagated 



by seeds, or by divisions. 



P. fertffls (f ertile). A synonym of P. palugtnt. 



P. palnstris (marsh-loving), fl.., inflorescence in airy, diffuse, 



purplish or violet-tinged panicles, rising to a height of from 



2jft. to 3ft. L long, soft, smooth, slender, arching, and forming 



dense tufts. Southern Europe, Ac. A very desirable species, 



and one of the best for forming dense, isolated tufts, near the 



banks of streams. Srx. P. fertilis. 



P. trivialis albo-vlttata (common white-striped). * A very ele- 

 warf, perennial grass, forming dense tufts of erect leaves, 

 are flat, and broadly margined with pure white. Though 

 ty of a hardy species, it is most 

 respect to its foliage, to be a very usef 



-. - 



gant, dwarf, perennial grass, forming dense tufts of erect leaves, 

 which are flat, and broadly margined with pure white. Though 

 a variety of a hardy species, it is most effective, and proves, in 

 respect to its foliage, to be a very useful decorative plant, when 

 grown in pots, under glass. A. 6m. 1868. (F. d. S. 1695.) 



POARCHON. A synonym of Trimezia (which 

 M0). 



POCOCXIA. Included under Trigonella (which 

 see). 



POCULIPOK.M. Resembling a drinking- cup or 

 goblet in shape. 



POD. -A several-seeded, dehiscent, dry fruit. The 



FIG. 209. THREB-VALVED POD OF YUCCA. 



term is more usually applied to a Legume or Siliqna. A 

 three-valved Pod of Yucca is shown at Fig. 209. 



