with Geographic Botany, — Temperature, 175 



of water, or 180°. These extremes of temperature for the 

 surface of the globe are indeed great, and they demonstrate 

 how wonderfully man is capable of adapting himself to cir- 

 cumstances, as beneath each he is able to exist ; nor does 

 there appear any reason why the vegetable kingdom should 

 not thrive beneath the same. Some persons, for experiment, 

 have exposed themselves to a greater degree of heat, and 

 without unpleasant results ; but this was only for a certain 

 time, and gives no idea of the effects of an habitual exposure 

 to such excitement. 



Observations on the condition of organized nature in the 

 hottest regions of the world will lead us to the conclusion, 

 that there is an intimate adjustment between the productions, 

 animal and vegetable, and the agency of external causes. If 

 the temperature were by any unforeseen circumstances to be 

 raised a few degrees, a corresponding change in the tempera- 

 ment and organization of the living beings would be necessary 

 for the proper fulfilment of their functions. A comparison of 

 different latitudes with each other, and the allotted produc- 

 tions of each, clearly manifest the intimate relations between 

 the climate and the vegetation, and the reluctance displayed 

 to leave the conditions under which they have been placed. 

 Many instances might be mentioned to prove, that the exact 

 circumstances acting on the vegetable kingdom are those the 

 most favourable to its existence ; it will be enough at present 

 to add, that similarity of climate does always support simila- 

 rity of productions ; that however distant the situations may 

 be, wherever similar external causes are active, there we shall 

 find similar states of organization. 



There are still some remarkable instances, at times noticed 

 by the naturalist, which demonstrate that vegetation does 

 thrive under unusual conditions. These cases are exceptions, 

 but not less interesting on this account, and show to what 

 extent the organs of plants can modify their functions under 

 the influence of unnatural circumstances. At present our at- 

 tention is confined to temperature, and many curious facts 

 have been noticed of plants appearing to thrive well in situa- 

 tions where the surface has been heated by internal fires, or 

 actually in hot springs themselves. One of the most inter- 

 esting, perhaps, of these circumstances is mentioned by Mr. 

 Barrow in his ' Voyage to Cochin-China.^ At the island of 

 Amsterdam, he observed a paste near some hot springs, the 

 temperature of which was 186° at eight inches beneath the 

 surface. On the top were growing a Lycopodium, a Mar- 

 chantia, and a small delicate moss, being members of three 

 natural families, but all agamic. In a hot spring at Gastein, 

 with a temperature of \\1°, Ulva thermalia .was found grow- 



