78 DR. V. MAKTIUS 



nature, if it were possible to force a proper degree of heat upon 

 plants by means of red-hot ovens placed at safe distances, or 

 increase the quantum of light by means of multiplied mirrors ; 

 but such schemes can only be imaginary. Solar heat will for 

 ever remain a desideratum in the cultivation of tropical or 

 untropical plants, which can only partially be realised, and we 

 can only approach the natural state of things by means of 

 bottom heat, producing a proper radiation, and aided by moisture 

 of a suitable temperature. If I err not, proper attention has 

 not always been paid in the construction of glass-houses to these 

 several sources of heat, the influence of the rays of light and of 

 warmth have been confounded together, especially as regards our 

 chief artificial medium, namely, ground heat. Our ancestors 

 used to derive great results from low forcing-beds ; I may notice, 

 among others, the rare exotics of Trew, which were I'eared in the 

 low manure and bark-beds of his little plant-house, and brought 

 to blossom and fruit in these. I saw the remnants of this 

 pariarchal simplicity some forty years ago at Nuremberg. So 

 also in regard to Jacquin, whose costly works bear witness to 

 great results obtained from comparatively humble means. 



It is known that the mean temperature of wells between the 

 tropics continues high all the year round. In the Villa da 

 Barra do Ilio Negi'o in the Amazon territory, I observed the 

 temperature of a well in the sandstone of a forest through twelve 

 days, at seven o'clock, and found its temperature to be 19° R., 

 and the prevailing ground temperature I should in no case rate at 

 a less degree. The Amazon water showed commonly 21° R., 

 and so do its grand tributaries near their sources. But the 

 stream constantly exposed to the rays of the sun, exhibited very 

 often the prodigious height of 37° to 40° R. It may be easily 

 concluded that the lands in those latitudes even of primeval forests 

 must have a constant high temperature. In some regions not 

 overgrown with forest, situated even beyond the tropics, the tempe- 

 rature was still higher, though not with the same constancy. Thus, 

 Sir J. Herschell has communicated to Dr. Lindley most impor- 

 tant observations made by him at the Caps of Good Hope.''' " On 

 the 5th of December, 1837, Sir John found that the temperature 

 of the earth in a bulb-garden was 159° F. between 1 and 2 in 

 the afternoon (= 56° 44 R ); at three o'clock i50°F. (= 52° 44 

 R.) ; and even in shady situations 1 1 9° F. ( = 38° 67 R.) ; while the 



Lindley's Theory of Horticulture, p. 99. 



