Megasea.—­This hardy herbaceous plant flowers from April to June.  A light, sandy soil suits it best.  It may be grown from seed or multiplied by division.  Height, 1 ft.

Melissa Officinalis.—­A hardy perennial, flowering in July.  Any soil suits it.  It is increased by division of the root.  Height, 1 ft.

Melittis Melissophyllum (Large-flowered Bastard Balm).—­This handsome perennial is not often seen, but it deserves to be more generally grown, especially as it will thrive in almost any soil; but to grow it to perfection, it should be planted in rich loam.  It flowers from June to August, and may be increased by division of the roots any time after the latter month.  Height, 11/2 ft.

Melon.—­Sow from January to June in pots plunged in a hotbed, the temperature of which should not be under 80 degrees.  When the plants have made four or five leaves, set them out in a house or hotbed having a temperature ranging from 75 to 85 degrees.  Keep the plants well thinned and water carefully, as they are liable to damp off at the collar if they have too much wet.  Do not allow them to ramble after the fruit has begun to swell, nor allow the plants to bear more than two, or at most three, melons each.  They require a strong, fibry, loamy soil, with a little rotten manure worked in.  The Hero of Lockinge is a grand white-fleshed variety, and Blenheim Orange is a handsome scarlet-fleshed sort.

Menispermum Canadense (Moon seed).—­A pretty slender-branched, hardy, climbing, deciduous shrub, with yellow flowers in June, followed with black berries.  It grows in any soil, and can be propagated by seed, by division of roots, or by planting cuttings in spring in a sheltered spot.  Height, 10 ft.

Mentha Rotundifloria Variegata (Variegated Mint).—­A hardy perennial, which may be grown in any soil, and is easily increased by dividing the roots.  It flowers in July.  Height, 2 ft.

Menyanthes.—­Treat as other hardy aquatics.

Menziesia (Irish Heath).—­This evergreen thrives best in fibrous peat to which a fair quantity of silver sand has been added.  While excessive moisture is injurious, the plant must not be kept too dry; the best condition for it is to be constantly damp.  Slips torn off close to the stem will root in sand under glass, placed in gentle heat.  Height, 2 ft.

Mertensia.—­These hardy perennials flower from March to July.  They will grow in any garden soil, but do best in peat, and are propagated by division.  They make fine border plants.  Mertensia Maritima and M. Parviflora, however, are best grown in pots, in very sandy soil, perfection being afforded them during the winter.  Height, 11/2 ft. to 2 ft.