Flower colour is not so fixed as leaf colour, for obvious reasons, the green colour of leaves being due to chlorophyll, which is an absolutely necessary ingredient of the leaf if plant food is to be manufactured; whereas flower colour is merely for advertisement, and any pigment can be made to serve. In nature most flowers vary in tint, and some in a marked degree--take the little native Milkwort (_Polygala_), which may be blue or purple or white. Flowers offer great opportunities, therefore, to the gardener, and by selecting on the one hand and hybridizing on the other every known tint has been reproduced in some blossom. Adding to this the variability in size and shape of petals, and the tendency to “doubling,” the flower in the hands of skilful cultivators has been altered almost beyond recognition. Take the Roses, for example, with their infinite variety of form and colour. The bulk of them are derived from a dozen wild species, possessing comparatively small single flowers, white, yellow, or red--_Rosa centifolia_, _damascena_, _gallica_ (the source of the older Roses), _indica_, _moschata_, _odorata_, _rugosa_, _Wichuræiana_, with our native _arvensis_ and _spinosissima_. By selecting for colour, shape, and “doubleness,” both from the species themselves and from the offspring produced by hybridizing one of these with another, what a wealth of beauty has been developed! More than any other flowers, the Roses are the crown and glory of the gardener’s art. Well has the Rose been called the Queen of Flowers; but it owes its royal prerogative to man. Nature provided blossoms--elegant, but of no special promise--and a tendency to vary, of priceless value; human skill and industry have done the rest. CHAPTER VII PAST AND PRESENT