442 Retrospective Criticism. 



made a point of supplying gardener's iron of good quality, at a reasonable 

 rate. — Superficial. Brixton Villa, June. 



Campanula, or Ipomcea cdrnea, you mention (p. 278.) as an annual ; is it 

 not rather a perennial ? Jacquin, in his Sclectaruni Stirjnum Americandrum 

 Historia, Manheim, 1788, p. 55. says: " Ex semine nata in caldario horti 

 Vindobonensis per^j/itresannosiaete vegetavit,altissima excrevit, sed tandem 

 sine ulla f'ructificatione interiit ;" and the plant which has been now flou- 

 rishing for upwards of two years at Mr. Pontey's, seems disposed to follow 

 its example, having shown no disposition to flower as yet. As, how- 

 ever, the life of many annuals is prolonged, when they have been prevented 

 from reproducing their species, it is possible that the Campanilla, being pre- 

 vented by change of climate from flowering, may be thus forced, contrary 

 to its natural habits, to become to a certain extent perennial. Can you 

 then inform me whether it really is annual or perennial, and whether it has 

 ever flowered in our hot-houses? What I have just said, brings to my re- 

 collection the method pursued in the West Indies, of artificially prolonging 

 the life of the Agave americana, which is frequently used for fences, and 

 dies as soon as it has completed its fructification, in which case gaps would 

 be occasioned in the fence formed with it; to prevent this, the planters cut 

 down the scape, or flowering stems, before it flowers; and by thus protracting 

 the fructification, protract, almost indefinitely, the decay of the plant. At 

 Barbadoes the Yucca aloTfolia is employed (planted in a single row) for 

 fences, in the same manner as the Agave in other islands, and the fences 

 so constructed appeared to me equally impervious to man and beasts. Of 

 their durability I know nothing. — W. Hamilton. Oxford Place, Plymouth, 

 August 6. 1828. 



Iron-roofed Hot-houses. — Your correspondent, Agronome (p. 310.), after 

 speaking in favour of iron-roofed hot-houses, says, " at the same time, I ac- 

 knowledge that ii'on decays very fast," &c., and seems desirous to be made 

 acquainted with a timber which might be advantageously substituted for 

 both iron and the timber at present in use. South America and the West 

 Indies abound in many timbers of this description, which, from strength, 

 hardness, and durability, are prefei'able even to iron, though, possibly, rafters 

 made of them may require a somewhat greater thickness. That whicli I con- 

 ceive most likely to answer is, the Zygophyllum arboreum, or Guayacan 

 tree, known also in the vicinity of Cumana by the names of Bera and Palo 

 sano, and at Carthagena by that of Palo santo. It is a tree of 40 ft. high, ac- 

 cording to Jacquin, producing, in July, a profusion of golden flowers, which 

 make, as Humboldt tells us, in his Personal Narrative, vol. iii. p. 8., a most 

 beautiful appearance, when viewed from the top of the hill of San Francisco. 

 Its timber is of large size, reddish colour, and close, fine, compact grain, ad- 

 mitting of being easily washed. The weight of the cubic foot is 70 lb. 10 oz. 

 294 grs., while a similar cube of African timber weighs 65 lbs. 10 oz. 21 grs., 

 and of best British oak 53 lbs. 49 grs., giving for their relative gravity, tak- 

 ing oak as the standard, Guayaca VSooS, African timber, 1'3238. and oak, 

 roooo. Of this timber, main timbers of houses eight stories high, in Guay- 

 aquil, are constructed, and last for an indefinite number of years, proving 

 both the extraordinary strength and durability of this timber, of which a 

 late Spanish writer, Don Jose Ignacio de Pombo, one of the friends of the 

 illustrious Mutis, and highly spoken of by Humboldt, in the sixth volume 

 of his Personal Narrative, says, in a treatise on the natural productions of 

 the province of Carthagena, that it is " tan compacta^ solida, y pesada como 

 el mismo hierro; y todos producen una resina que tiene las mismas virtudes 

 de su madera ; y que baxo delagua se conviertan en piedra;" and Jacquin 

 adds to his account, " Incolis dicitur Guayacan, quo apud illos generico no- 

 mine appellantur omnia ligna dura materiaturae aptissima. Fertur ipsius 

 truncus, sub terra sepultus in lapidem rautari, nee unquam corrumpi." From 

 its united qualities of strength, size, and durability, I have been led to re- 



