CHAPTER OF VARIETIES. 505 



higher and colder shores of Europe. It is in the south, in the latitude 

 of Madeira, that the opaline coloured mollusca are most common. In 

 consequence of their prevalence in this part of the Atlantic, the English 

 sailors give them the name of Portuguese men of war. Humboldt, in 

 noticing them in his Narrative, says, that when he had passed the lati- 

 tude of 36 he entered the Azores, in which the whole sea was covered 

 with a prodigious quantity of them. The vessel was almost becalmed, 

 but the mollusca advanced towards the s. E. with a rapidity equal to 

 four times that of the current, and continued to pass for three quarters 

 of an hour. Here he recognised three species, the Medusa aurita of 

 Baster, the M. pelagica of Bosc, and a third which approached the 

 M. hysocella, distinguished by its yellow-brown colour, and its tentacula 

 longer than its body. They are one of the sources of the phosphores- 

 cence of the ocean. By Humboldt's experiment they emitted light 

 when shaken. Placed on a tin plate, the vibration of the tin when 

 struck was sufficient to make the irritated animal shine. R. H L. 



VEGETATIVE PECULIARITIES IN DURABLE AND SOFT WOODED 

 TREES IN THE TROPICS. In the temperate zone, those trees which 

 change their foliage with the seasons, shedding their leaves as the 

 winter comes on, and standing with bare branches through a succession 

 of weeks, if hard and solid timber trees, are notoriously of slow 

 growth, and require years, in some cases ages, to mature the texture of 

 their fibres. This is the case with the oaks and elms. Where, how- 

 ever, vegetation is never checked by hibernation, as in most trees in the 

 tropics, and in the evergreens of temperate climates, woods may be of 

 quick growth, and have all the characters of durability, weight, and 

 compactness. The Acacia batriahonda, which yields a more solid and 

 durable timber than any European tree, arrives at maturity in fifteen 

 or twenty years, and is never leafless ; whilst the ceiba or silk-cotton- 

 tree (Bombax pentandra), a very giant of the forest, and the gomier 

 (Busera gummifera), a tree of good size and bulk, showing their golden 

 foliage every year, are the softest of all tropical woods used for domestic 

 or constructive purposes. The one is scooped into canoes, for which its 

 large growth and light texture admirably adapt it ; the other is formed 

 into bowls and small gamelles, for which its facility of being worked, 

 and its clean whiteness render it highly suitable. The dye woods, 

 which are all woods of hard flinty fibre, suffering no hybernation, are 

 of rapid growth ; such are the logwood (Hematojcylum Campechianum) , 

 the fustic (Morus tinctoria), and the braziletto (Ccesalpiniavesicarid), 



VOL. i. NO. xi. (NOVEMBER, 1833.) Q 



