INFLUENCE OF TEMPERATURE ON VEGETATION. 6 'I 



would seem not to be injurious. Of ninety-four experiments which were made by 

 Tarnowsky with all possible precautions ^ the result was that the spores of Fem- 

 ciUiinn glauciim and Rhizopus nigricans exposed for from one to two hours to air 

 of a temperature betvv^een 70° and 80° C. germinated only very rarely, while a 

 temperature of 82° or 84° C. altogether killed them. Spores heated in their proper 

 nutrient fluids nevertheless entirely lose their power of germination at 54° or 55° C.^ 



The growth of parts of the embryo at the expense of the reserve-materials 

 begins, as my experiments show^ in the case of wheat and barley even below 50° C; 

 in Phaseolus j7iultiflorus and Zea Mais at (f-^, C. ; in Cucurbita Pepo at 13°- 7 C. But 

 when the reserve-materials of the seed have been consumed, a higher temperature is 

 apparently always necessary to enable growth to proceed at the expense of freshly 

 assimilated material. The highest temperatures at which my observations indicate 

 that germination can take place were about 42° C. in the case oi Phaseolus mulfiflorus, 

 Zea Mais, and Cucurbita Pepo; in wheat, barley, and peas about 37° or 38° C. 



The lowest temperature at which the grains of chlorophyll turn green was 

 determined for Phaseolus inultiflorus and Zea Mais at above 6° and probably 

 below i5^C. ; for Brassica Napus above 6°C. ; for Pimis Pinea between 7° and 

 ii°C. The highest temperature at which leaves already formed and still yellow 

 turn green was for the first-named plants above 33""; for Allium Cepa above 36"" C. 



The exhalation of oxygen and the corresponding assimilation begin, according 

 to Cloez and Gratiolet, in the case of Potamogeton between 10° and i5°C. ; in 

 Vallisneria above 6°C. In many Mosses, Algai, and Lichens, assimilation may 

 possibly take place at still lower temperatures ; according to Boussingault (Compt. 

 rend. vol. 68, p. 410), carbon dioxide is decomposed by the leaves of the larch 

 at o°-5 to 2°-5 C, and by those of meadow-grasses at i°-5 to 3°'5 C. The upper 

 limit of temperature for this function has not been ascertained. 



The sensitiveness and periodical movement of the leaves of oMimosa do not 

 begin till the temperature of the surrounding air exceeds i5°C. ; the periodical 

 movements of the lateral leaflets of the leaf of Desmodium gyrans only at tem- 

 peratures above 2 2°C. The upper limit of temperature for the sensitiveness of the 

 leaves of Mimosa depends on the continuance of the warmth ; in air of 40^ C. 

 they become rigid within an hour; at 45° C. within half an hour; at 48° to 50° 

 within a few minutes, but may again become sensitive when the temperature falls. 

 A temperature of 52° C. causes permanent loss of the power of motion, and death. 



The lower limit of temperature for the motility of the protoplasm in Nitclla 

 syncarpa is stated by Niigeli to be zero ; for the hairs of Cucurbita my observations 

 place it at a temperature of 10° or ii°C. The upper limit is 37° C. in the case of 

 Nitella syncarpa according to Nageli ; in the hairs of Cucurbita, when immersed in 

 water of 46° or 47° C, the current is arrested within two minutes ; in the air exposure 



» One of the most important of these precautions is to prevent with certainty the entrance of 

 spores after the temperature has been raised in the apparatus to the required point. 



- For further details see pt. Ill of the Proceedings of the Botanical Institute of Wiirzburg. 



3 Sachs, Abhangigkeit der Keimung von der Temperatur, Jahrb. fiir wissensch. Bot. vol. II, 338, 

 i860.— A. De Candolle in Bibliotheque universelle de Geneve 1865, vol. XXIV, p. 243 et seq.-~ 

 Koppen, Warme und Pflanzenwachsthum, eine Dissertation, Moscow 1870.— See also further under 

 chap. IV. 



