Hydra was of no importance in ancient times. The only fact in its history is that the people of Hermione (a city on the neighbouring mainland now known by the common name of Kastrï) surrendered it to Samian refugees, and that from these the people of Troezen received it in trust. It appears to be completely ignored by the Byzantine chroniclers. In 1580 it was chosen as a refuge by a body of Albanians from Ko⅛inyas in Troezenia; and other emigrants followed in 1590, 1628, 1635, 1640, &c. At the close of the 17th century the Hydriotes took part in the reviving commerce of the Peloponnesus; and in course of time they extended their range. About 1716 they began to build sakturia (of from 10 to 15 tons burden), and to visit the islands of the Aegean; not long after they introduced the latinadika (40-50 tons), and sailed as far as Alexandria, Constantinople, Trieste, and Venice; and by and by they ventured to France and even America. From the grain trade of South Russia more especially they derived great wealth. In 1813 there were about 22,000 people in the island, and of these 10,000 were seafarers. At the time of the outbreak of the war of Greek independence the total population was 28,190, of whom 16,460 were natives and the rest foreigners. One of their chief families, the Konduriotti, was worth £2,000,000. Into the struggle the Hydriotes flung themselves with rare enthusiasm and devotion, and the final deliverance of Greece was mainly due to the service rendered by their fleets.

See Pouqueville, Voy. de la Grèce, vol. vi.; Antonios Miaoules, Υπόμνημα πepι της vησoυ Ύδρας, Munich, 1834; Id., Συνοπτική ιστορία των ναυμαχιών δια των πλοίων των τριών νήσων, Ύδρας, Tleτσωv, και Ψαρών, Naιιplia, 1833; Id., Ιστορία της νήσου Ύδρίις, Athens, 1874; G. D. Kriezes, Ιστορία της νήσου Ύδρας, Patras, 1860.

There are upwards of thirty species, found chiefly in Japan, in the mountains of India, and in North America, and many of them are familiar in gardens, H. Hortensia is the most useful for decoration, as the head of flowers lasts long in a fresh state, and by the aid of forcing can behad for a considerable period for the ornamentation of the greenhouse and conservatory. Their natural flowering season is towards the end of the summer, but they may be had earlier by means of forcing. H. japonica is another fine conservatory plant, with foliage and habit much resembling the last-named, but this has flat corymbs of flowers, the central ones small and perfect, and the outer ones only enlarged and neuter. This also produces pink or blue flowers under the influence of different soils.

The Japanese species of hydrangea are sufficiently hardy to grow in any tolerably favourable situation, but except in the most sheltered localities they seldom blossom to any degree of perfection in the open air, the head of blossom depending on the uninjured development of a well-ripened terminal bud, and this growth being frequently affected by lite spring frosts. They are much more useful for potculture indoors, and should be reared from cuttings of shoots having the terminal bud plump and prominent, put in during summer, these developing a single head of flowers the succeeding summer. Somewhat larger plants may be had by nipping out the terminal bud and inducing three or four shoots to start in its place, and these, being steadily developed and well-ripened, should each yield its inflorescence in the following summer, that is, when two years old. Large plants grown in tubs and vases are fine subjects for large conservatories, and may be used for decorating terrace walks and similar places during summer, being housed in winter, and started under glass in spring.

The Indian and American species, especially the latter, are quite hardy, and some of them are extremely effective. The finest of these by far is the Hydrangea paniculata grandiflora, the branched inflorescence of which is under favourable circumstances a yard or more in length, and consists of large spreading masses of crowded white neuter flowers which completely conceal the few inconspicuous fertile ones. The plant attains a height of 8 to 10 feet, and when in flower late in summer and in autumn is a very attractive object in the shrubbery.