728 GENERAL CONDITIONS OF PLANT-LIFE. 



1 87 1, no. 12) observed the remarkable fact that seeds of Acer plaianoides and of 

 Wheat which had fallen between pieces of ice in an ice-house germinated there 

 and pushed a number of roots several inches deep into the fissureless pieces of ice. 

 From this observation he concluded that these seeds had the power of germi- 

 nating at or even below the freezing-point of water; and that the penetration of 

 the roots into the ice is caused by the development of warmth in the seed and by 

 the pressure of the growing roots. It seems to me however that another expla- 

 nation is possible. The ice was evidently surrounded by warmer substances, such 

 as the walls of the house, which emitted to it rays of heat. Now it is a well-known 

 fact that rays of heat, when they strike upon bubbles of air or bodies firmly frozen 

 into a piece of ice, warm them and melt the surrounding ice. In this way not 

 only the seeds but also their roots were warmed by the radiation of heat which 

 passed through the ice, and thus the particles of ice in contact with them were 

 melted. This experiment gives us therefore no certain knowledge of the actual 

 temperature of the germinating seeds. The statements of different observers as to 

 the highest temperature of the water in which some of the lower Algae grow vary 

 greatly ; and Kegel's assertion is perhaps the most probable that water must be 

 below 40° C. for plants to grow in it. I have convinced myself that a considerable 

 number of plants are killed by an immersion for only ten minutes in water of 45° or 

 46° C, while flowering plants endure for a longer period an air-temperature of 48° 

 or 49° C; but at 51° C. lose their vitality after from ten to thirty minutes (any 

 possible injury by drying up being of course prevented) ^ As to the high tem- 

 peratures which the spores of Fungi can endure without losing their power of ger- 

 mination, very different statements, some of them altogether incredible, have been 

 made, according to which temperatures of more than 100°, even as high as 200° C, 

 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 Peni- 

 cilliutn glaucum and Rhizopus nigricans exposed for from one to two hours to air 

 of a temperature between 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 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 5°C.; 



^ H, de Vries, Materiaux pour la connaissance de I'influence de la temperature, in Archives 

 Neerlandaises, vol. V, 1870, arrived at the same results from a number of experiments on Crypto- 

 gamia and flowering water and land-plants. According to Schmitz (Linnsea, 1 843) Sphceria carpophila 

 is killed in ten minutes by water of 35°-38° R. (43-5°-47-5° C). 



^ 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. 



According to Wiesner (Sitzber. d. Wien. Akad. 1873) spores of PenicilUtim glaucum sown on 

 lemon pulp will not germinate below 1*5° C. or above 43° C. Any further development is confined 

 to narrower limits. The most favourable temperature is from 22° to 26° C. 



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



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

 i860. — A. De Candolle in Bibliotheque universelle de Geneve, 1865, vol. XXIV. p. 243^/5^7. — 

 Koppen, Warme und Pflanzenwachsthum, eine Dissertation, Moscow 1870. — According to Kerner 

 (Nat. wiss. Verein Janobrock, 1872) most plants, especially alpine plants, can germinate below 2° C. 

 See also further under chap. IV. 



