Plums.—­Almost any soil will grow this useful fruit.  Young trees may be planted at any time, when the ground is friable, from November to March, but the earlier it is done the better.  The situation should be somewhat sheltered.  In exposed positions protection may be afforded by a row of damson trees.  Many varieties are suitable for growing on walls or sheds, where they are trained into fans, as cordons, and other decorative designs; but it must not be overlooked that until the trees are well established a great deal of fruit is necessarily lost by the severe pruning and disbudding which is required to bring the tree into shape.  A pyramid-shaped tree is useful, and is easily grown by training one straight, central shoot, which must be stopped occasionally so that fresh side branches may be thrown out, which of course must be kept at the desired length.  A bush tree about 7 ft. in height is undoubtedly the best form of growth, and needs but a minimum amount of attention.  In pruning wall trees the main object is to get the side-shoots equally balanced, and to prevent the growth advancing in the centre.  The bush form merely require the removal of any dead wood and of cross-growing branches.  This should be done late in the summer or in the autumn.  The trees are frequently attacked by a small moth, known as the Plum Fortrix, which eats its way into the fruit and causes it to fall.  In this case the fallen unripe fruit should be gathered up and burned, and the trees washed in winter with caustic potash and soda.  For growing on walls the following kinds may be recommended:  Diamond, White Magnum Bonum, Pond’s Seedling, and Belle de Louvain for cooking; and Kirke, Coe’s Golden Drop, and Jefferson for dessert.  For pyramids and bushes, Victoria, Early Prolific, Prince Engelbert, Sultan, and Belgian Purple are good sorts.  In orchards Plums should stand 20 ft. apart.

Poa Trivalis.—­A very pretty, dwarf-growing, variegated grass.  Plant in a moist situation in a rich, light, loamy soil.  It is increased either by seed or division.

Podocarpus.—­See “Cephalotaxus.”

Podolepis.—­Hardy annuals bearing yellow and red and white flowers.  A mixture of loam and peat is most suitable for their growth.  They are easily raised from seed sown in March, and bloom from June to August.  Height, 1-1/2 ft.

Podophyllum Peltatum (Duck’s Foot, or May Apple).—­Grown chiefly for its foliage and berries, this hardy herbaceous perennial forms a pleasing spectacle when planted in moist soil under trees; it likewise makes a splendid pot-plant.  A mixture of peat and chopped sphagnum is what it likes.  The pots are usually plunged in wet sand or ashes on a northern border.  It is propagated by cutting the roots into pieces several inches in length, with a good bud or crown on each.  During May and June the plant produces small white Dog-rose-like flowers.  Height, 1 ft.

Poinsettia Pulcherrima.—­A stove evergreen shrub which produces lovely crimson bracts in the winter.  Plant in sandy loam, give plenty of water to the roots, and syringe the leaves frequently.  In early spring cut down the branches to within three or four eyes of the old wood.  These cuttings, if laid aside for a day to dry and then planted under glass, will form new plants.  It flowers in April.  Height, 2 ft.