This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
This favourite genus is distinguished as follows: Calyx 5-lobed; lobes simple or compound, inserted upon the top of a spherical or pear-shaped calycinal tube, generally considered as a mere dilatation of the flower-stalk; corolla normally of 5 petals alternating with the calyx-lobes, but very susceptible of duplification through the transformation of some or all of the stamens into petals; stamens indefinite in number, often exceeding a hundred, inserted around the circumference of the receptacle, within the petals; carpels more, or less numerous, according to the species (5 to 60), uniovulate, inserted at the base and upon the walls of the calycinal tube, each with a simple style and stigma projecting beyond the mouth of the tube. The ripe fruit of the Rose, consisting of many- 1-seeded carpels within a more or less fleshy tube, is analogous in organic structure to the inferior fruit of the Pomacece,
Roses are woody erect or more or less climbing or trailing thorny shrubs, generally spreading by suckers from the roots, with compound stipulate leaves, excepting one species, R. berberidifolia, which has simple or reduced leaves, and is considered by some botanists as forming the type of a distinct genus. The leaves of the majority of the species are deciduous; but some retain their foliage so far into the winter as to entitle them to be classed with evergreen shrubs.
The flowers of Roses present us with an endless variety of tints, ranging from pure white to dark purple, though no variety or species is known with scarlet flowers, and there is not the slightest approach to blue, nor is it likely that cultivators will ever succeed in producing a variety of that colour. By way of compensation, however, we have many bright yellow species, from which, by variation and skilful crossing with other colours, some of the most delicate salmon, flesh, cream, and other shades have been obtained. Another, though rare, variation in the colouring of Roses is seen in some striped sorts, where white and carmine or lilac are combined; but hitherto the yellow ones have not shown this peculiarity.
A very important quality possessed by most if not all species of Roses under cultivation is to become more or less double by ' the transformation of the stamens into petals. This tendency seldom exhibits itself when the plant is in its wild state, but nothing is more frequent when the plant is transferred to a richer soil. In most instances the transformation of the stamens is only partial, but occasionally total, causing the flowers to become barren, unless fecundated by foreign pollen, for the disappearance of stamens does not necessarily involve the absence of ovaries. According to the degree of this transformation Roses are termed semi-double, double, or very double or full. And the fuller or more double a rose is, the greater is its value from a horticultural point of view, though in reality it is a monstrosity.
At the present time upwards of thirty botanical species are known, all belonging to the northern hemisphere - from Kamtschatka and Japan to the western shores of Europe, and in smaller numbers from North America. No species is known south of the equator, in fact few pass the 25th degree of North latitude. The actual southern limits of the genus are in the Indian peninsula, Abyssinia, and Mexico. All are hardy in the South of Europe, and the tenderest require but slight protection even in England. The specific forms, or those forms considered as such, in this very homogeneous and distinct genus are, on the contrary, so closely allied and so variable in themselves that their determination has ever been the Grordian knot of botanists. In spite of the greatest efforts and researches, the limits of specific groups and the characters upon which they should rest are still matters of discussion. Hence follow great confusion and uncertainty with regard to the number and distribution of the species. But this confusion is as nothing compared with that caused by horticulturists, whose innumerable crossings and re-crossings of species and varieties have resulted in the almost total obliteration of the original forms, so that it is now utterly impossible in this chaos of varieties to recognise their specific types. A glance at the catalogues of our principal Rose growers is sufficient to discover that the groups into which they divide their species and varieties are for the greater part purely arbitrary aggregations.
In no other genus are there so many hybrids as in this. Every year our nurserymen offer new sorts, and at the present time one might easily enumerate a thousand varieties said to be of hybrid origin, of which, however, we have in few cases positive proof.
As we have previously remarked, the greatest uncertainty still exists respecting the limits of the botanical species of this genus. What is considered by one monographer as a good species is reduced to a simple variety by another. In the following enumeration, therefore, we can only set forth opinions, but with due care to range ourselves with those which appear most probable. For our guide we believe we cannot do better than take Lindley's monograph, which appeared upwards of fifty years ago, but subsequent publications have added very little to it.
Dr. Lindley divided Roses into eleven tolerably natural tribes, though in some cases the differences are very slight. They are as follow :