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GENERAL CONDITIONS OF PLANT-LIFE. 
187 1, no. 12) observed the remarkable fact that seeds of Acer platanoides 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- 
cilliiun 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, 1843) 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 Penicillium glaucum sown on 
lemon pulp will not germinate below i'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 Würzburg. 
* Sachs, Abhängigkeit der Keimung von der Temperatur, Jahrb. für wissensch. Bot. vol. II. p. 338, 
i860. — A. De Candolle in Bibliotheque universelle de Geneve, 1865, vol. XXIV. p. 2 ^■^ et seq. — 
Koppen, Wärme und Pflanzen wachsthum, eine Dissertation, Moscow 1870. — Accoiding to Kerner 
(Nat. wiss. Verein Janobrock, 1872) most plants, especially alpine plants, can germinate below 2° C. 
See also fuither under chap. IV. 
