Pimpernel.—­See “Anagallis.”

Pinguicula Grandiflora (Great Irish Butterwort).—­This handsome, hardy bog-plant produces deep violet-blue flowers in August and September.  It may be grown in any damp soil and increased by division.  Height, 1-1/2 ft.

Pinks.—­Will live in almost any soil, but if large blooms are required rich earth is essential.  They are increased by pipings taken in May or June.  These should be planted out in October, but must be given a well-drained position, as too much wet is injurious to them.  Do not set the roots too deep, but let the collar of the plant be on a level with the soil.

Pinus.—­As a tall specimen tree nothing is more graceful than the Corsican Pine (Pinus Laricio).  P. Strobus Nana is a curious dwarf variety, rarely exceeding 3 ft. in height.  The Argentea Aurea is also of dwarf habit.  Its leaves, which are green in summer, change to a bright golden colour in winter.  The Umbrella Pine (Sciadopitys) is a very striking conifer, and does well everywhere.  It gets its name from its leaves being set at regular intervals round the branches, like the ribs of an umbrella.  The Pinus may be increased by layers, or by sowing the cones in spring, after they have opened out, in rather sandy soil, covering them lightly.

Piping.—­This consists in drawing out the young grass, or shoots, from the joints of Pinks, etc., from May to July being the time for doing so.  Place them in light, sandy soil, and cover them with a hand-glass.  Towards the end of September they may be planted out in beds or potted off in rich, light loam.  In either case they must not be planted too deeply.  The crust of the soil should be level with the collar of the plant.  If the pots are put into a frame the plants will require very little water during winter, but as much air should be given as is possible.  In March re-pot them, using 8-1/2-in. pots.

Platycodon (Japanese Balloon Flower).—­Hardy and elegant herbaceous plants, requiring a sandy soil.  They may be raised either from seeds or from cuttings of the young growth; they flower in July.  Height, 1 ft.

Platystemon Californicus.—­Pretty hardy annuals which thrive in a sandy soil.  They are easily raised from seed sown in March or April, and bring forth their flowers in August.  Height, 1 ft.

Pleroma Elegans.—­A beautiful evergreen shrub for a greenhouse.  Pot in equal parts of loam, peat, and sand.  It flowers in July.  Cuttings may be struck in peat in a rather warm temperature.  Height, 4 ft.

Plumbago.—­These pretty evergreens will grow in any soil, and can be propagated in September by cuttings of half-ripened wood having a heal, planted in a sandy soil, and kept near the glass in a greenhouse.  They flower in June.  Height, 3 ft.  P. Occidentalis is a charming greenhouse climber.  P. Capensis Alba is a greenhouse evergreen shrub, flowering in November, and growing to a height of 2 ft.  P. Larpentae is good for a sunny border, in light soil:  it bears terminal clusters of rich violet-purple flowers in September.  Height, 1 ft.  Plumbagoes require very little attention in winter.