Chap. II] HEAT 43 



other hand, in European warm springs they appear only after the water 

 has become much cooler — according to Agardh and Pfeffer, in the hot 

 springs at Carlsbad only when the temperature is down to $J° ; according 

 to Hoppe-Seyler, on the edge of fumaroles in water-vapour at about 6o° C. 

 I myself saw in Java, on the edge of fumaroles, even plants of a high 

 order, such as Rhododendron javanicum, flourishing vigorously in hot 

 vapour ; but I can give no accurate details in regard to the indubitably 

 high temperatures prevailing there. 



Under the influence of the sun's rays the temperature of the superficial 

 layers of soil in deserts attains a height which approaches the upper limits 

 for all plant-life, and is endured only by those parts that are poor in water. 

 Kerner says : 



' The crustaceous lichens, which adhere to the limestone rocks on the shadeless 

 desert of Karst in Istria and Dalmatia, are on cloudless days in summer constantly 

 exposed for many hours to a temperature of 58°-6o° C. without suffering any 

 consequent injury, and the manna lichen (Lecanora esculenta), as well as the rock 

 to which it is attached in the desert, is often heated up to 70 C. without perishing. 

 In addition, seeds that are embedded superficially in the desert sand, and there live 

 through the long period of drought, certainly assume the temperature of their 

 surroundings, which at midday is regularly 6o°-yo° C. The highest temperature 

 in superficial layers of soil has been observed near the Equator at the station 

 Chinchosho on the Loango coast. In very many cases it exceeded 75 , often reached 

 8o°, and once even 84 C. Even in this soil, annuals were not wanting during the 

 rainy season.' 



Pechuel-Losche l records a temperature of 69 C. in the sand of the seashore 

 on the Loango coast, close to an Ipomoea in full flower. 



Even air-temperatures scarcely lower than those of hot springs have 

 been observed in countries in nowise destitute of vegetation. Thus the 

 absolute maxima given by Blandford 2 for the year 1879 m India are for 

 Calcutta 41-1°, Benares 47-8°, Lahore 50-9°, Multan 52-8° C. As Hann, 

 from whose Climatology these figures are taken, states, air-temperatures 

 of 50 C. are not rare in the Punjab, even when the thermometer is 

 properly set 3 . With such air-temperatures in the shade, parts of plants 

 exposed to the sun's rays have to bear heating up to 6o°-jo° C, which is 

 a much more considerable degree of heat than the upper zero previously 

 observed. Thus Askenasy observed that with a temperature of 28 C. in 

 the shade the leaves of Sempervivum alpinum exposed to the sun attained 

 a temperature of 52 C. Such differences between the temperatures in 

 the sun and in the shade are exhibited certainly by succulent plants 

 alone, for the same observer found that the leaves of Gentiana cruciata, 



1 Pechuel-Losche, op. cit. p. 65. 



2 Blandford, Meteorology of India. Calcutta, 1881. 



3 Hann, Handb. der Klimatologie, ed. 1, p. 265. 



