I837-] Extra- Tropical Plants within the Tropics* 



293 



The authors, having shown, in a previous memoir, that the germina- 

 tion of the seeds of both monocotyledonous and dicotyledonous 

 plants was not prevented,' other circumstances being' favourable, 

 by exposure to a temperature of 112° Fahrenheit, were led to en- 

 quire whether the more common European Cerealiae (edible corn) 

 might not be cultivated successfully in the very warm climates. On 

 this point they found great discrepancy of opinion between 

 practical agriculturists equally, conversant with the history and 

 practice of agriculture, and scientific travellers who had visited such 

 climates: the former, maintaining their belief that they might be suc- 

 cessfully cultivated in all hot countries ; the latter, denying, from actual 

 observation, that they would succeed generally in tropical climates. To 

 determine this point, samples of the two principal varieties of wheat in 

 common use in France, the winter and spring varieties, were sown side 

 by side on the 23d April, in a piece of well prepared ground, the in- 

 creasing heat of the season being then very decided. Both germinated 

 alike, and for some time advanced equally. By and bye the heat in- 

 creased, and a remarkable difference became evident ; for, while the 

 spring wheat continued erect, its stems elongating and advancing in the 

 usual manner to ear, those of the winter wheat ceased to increase in 

 length, began to decline from the erect position, and the short stems 

 became hid in tufts of large leaves ; in a word it remained en herbe. In 

 this form they continue to vegetate vigorously, producing numerous 

 short stems, and large succulent leaves, forming together a beautiful 

 green plot, £he spring variety arrived at maturity at the usual time ; 

 when the change in the winter wheat commenced, the heat had risen 

 to about 66° Faht. ; whence the authors infer that this variety is incapa- 

 ble of arriving at maturity in any country, the mean temperature of 

 which exceeds 65» Faht. The next experiment seems strongly corobo- 

 rative of this deduction. A fresh portion of spring wheat was sown in 

 July, when the mean temperature had risen to 71 Faht., and underwent 

 the same changes that the winter wheat sown in spring had previously- 

 done ; that is the stems ceased to elongate, became oblique and depress- 

 ed, and were enveloped in tufts of large leaves, simulating luxuriant pas- 

 ture or turf. Hence it is further inferred, that the spring variety can 

 only be cultivated successfully in a climate the mean temperature of 

 which is under 71° Faht. In confirmation of these deductions from ex- 

 periment, the following facts are cited from the works of Boussingault 

 and Humboldt. The former of these travellers states that, in the whole 

 of the zone embracing the foot of the Andes, from the level of the sea 

 to the height of 1721 metres (nearly 6500 feet), he neither found wheat 

 nor barley, but, immediately above, he entered a broad zone presenting 

 abundance of thriving corn. The first of these zones has for its infe- 



