223 



undigested experiments made on the Arachis hypogcea, or " ground nut ;" and 

 his conclusions are, as might be expected, meagre and unsatisfactory : namely, that 

 darkness may be necessary to perfect the maturity of the pod, and that it may 

 further absorb " something" from the earth, and this " something" may be water. 

 To those who have attended to the phenomena of this extraordinary plant, the 

 true cause is evidently to secure the uniformity of temperature maintained by 

 terrestrial warmth. The temperature of the earth and the air are very diffe- 

 rent : that of the former will remain comparatively uniform during the night, 

 whereas the latter will be subject to incessant vicissitudes. It is thus that, in a 

 medium of uniform temperature, immature seeds may be ripened ; and in this 

 manner have I matured the green fruit of the Bannana : a thousand proofs might 

 be adduced in verification. The Colchicum autumnale ripens its seed-vessel and 

 contents below the surface of the ground, and if circumstances do not permit the 

 cyclamen to bury its seeds for the same purpose, it is interesting to observe how 

 carefully it coils the stalk round the vessel, so as effectually to conceal it ; not 

 merely to shroud it in darkness, but to preserve externally the uniformity of tem- 

 perature maintained by the plant. 



On the same principle are similar phenomena developed in aquatic vegetation. 

 The Ranunculus aquatica matures its seeds below the surface, the Valisneria 

 spiralis retracts its seed-vessels to the bottom of the river, and the Nelumbium, 

 Nymphea, and Nuphar withdraw their seed-vessels from the surface, to escape 

 from the effects of radiation, and take advantage of a medium comparatively 

 unchangeable and free from those alterations to which the aerial medium is con- 

 stantly subject. Sometimes bags or bladders of air fulfil the purpose of insulation, 

 as in the seed-vessels of the Passijlora cerulea and Colutea frutescens ; at other 

 times, silk and cotton are the means employed ; examples are supplied in the 

 Asclepias Syriaca, Gessypium hei'baceum, and " Silk-cotton Tree." We have 

 an evident proof that this is the intention, or at least the inference amounts to 

 probability, in the fact that we meet with the same provision in denizens of the 

 desert, between the tropics, as in arctic and antarctic lands ; thus, the seeds of the 

 Stapelia are enveloped in a silky down, as well as those of the Lilliputian Wil- 

 lows, on the shores of West Greenland. 



The Economy of Bulbs. 



Under this section it is not my intention to enter upon a description of the 

 various structures presented by bulbs, or the different offices or functions they are 

 destined to fulfil. My task, at present, will be confined to the provisions in their 

 economy to meet extraordinary contingencies. The distillatory function of the 

 Calla JEthiopica and Agapanthus umbellatus will be remembered; but the 

 change of place or position is not less remarkable. While plants generally 



