At first sight, therefore, the existence of flowers such as the violet, the buttercup, and the honeysuckle in an island south of the equator, and surrounded by vegetation of a totally different order, appeared to be so inexplicable that the hypothesis of a separate and distinct origin was advanced. A more satisfactory explanation has, however, been furnished by Darwin, which is now generally accepted. Very briefly, this is as follows. It is supposed that at the time of the glacial epoch the depression of temperature was so great as to admit of the prevalence in the tropics of forms of plants now peculiar to the temperate regions of the north. As the heat increased, such plants retreated from the tropics, for the most part northwards, but not exclusively. Following the snow-line, they also climbed to the cool heights of the lofty mountains of Central India and of Abyssinia, and even crossed the equator. They now linger upon the summits of the Javan mountains, and furnish by their presence an additional proof of the original union of the western islands of the Archipelago with the continent of Asia. During his stay at Buitenzorg, Mr. Wallace ascended the mountains Pangerango and Gedé. He describes this expedition as "by far the most interesting incident" of his visit to Java, and gives a full account of the various European plants which he found growing at different altitudes. In particular he mentions the royal cowslip (_Primula imperialis_), "which is said to be found nowhere else in the world but on this solitary mountain summit," and the stem of which he found sometimes growing to a height of over three feet. The list of families of European plants growing upon Pangerango and Gedé given by another scientific traveller, Mr. Motley, includes, among others, such familiar names as the violet, the buttercup, the primula, the lily of the valley, the honeysuckle and the wood-sorrel. I have already mentioned the fact that it is found possible to grow all European plants (but not fruits) in the mountain garden which is established on the slopes of Gedé, and which forms part of the Government gardens.