ESTIMATION OF THE HEAT NECESSARY TO GROWTH. 557 



certain others, so thei-e is a temperature for the protoplasm of every species at 

 which it freezes, anil another at which it is burnt. But tliis leads to the conclusion 

 that the molecules and groups of molecules in all protoplasm vibrate detinitely as 

 to extent and intensity so long as the protoplasm is living, even if it is not exactly 

 performing that woi-k which appears to us as growth — in other words, that a 

 definite amount of heat is necessary to the maintenance of life even in protoplasm 

 apparently resting; and that consequently it is not correct to suppose that all the 

 heat supplied to the plants is used up in growth. 



ESTLMATION OF THE HEAT NECESSAEY TO GROWTH. 



According to the mechanical theory of heat, which gives the best explanations 

 of numerous phenomena of life, all motion can be converted into heat, and measured 

 as such. Should it not be po.ssible to apply this principle to the vegetable kingdom, 

 especially to the phenomena of growth? Ought we not to be able to estimate 

 definitely how much heat is required for plants for each of their performances 

 within a definite period, and therefore to determine their heat-requirement as a 

 constant numerical quantit}'^? This question has often been put, and experiments 

 have not been wanting to supply the answer. It would not be only of theoretical 

 but also of great practical value, to be able to tell how much heat our forest trees, 

 our cei-eals and other economic plants, need for the accomplishment of their yearly 

 cycle of life, to know how much heat is necessary for the germination of this or 

 that cultivated plant, how much in order that the germinated plants may blossom, 

 and what degree of heat they require to produce ripe seeds of full weight and 

 capable of germination. If it were practicable to determine those quantities of 

 heat, which might be called the thermal constants of vegetation, we should be 

 able to estimate beforehand from the heat-conditions prevailing in any particular 

 place, whether this or that plant species would thrive, whether it could produce 

 ripe fruits, and whether or not its cultivation would be advantageous and worthy 

 of encouragement. 



Hitherto the results obtained in this direction leave very much to be 

 desired, but are nevertheless so interesting that they cannot be passed over in 

 silence here. First of all, it has been proved with regard to the earliest 

 phases of growth, the germination of spores and seeds, that not a few species are 

 able to germinate even at very low temperatures. The seeds of the White 

 Mustard, of hemp, of wheat and rye, of the Norway Maple, and of the wild 

 violet, germinate at a temperature very near freezing, between 0° and 1°C.; others, 

 such as the garden cress, flax, spinach, onions, poppy, beet-root, and the English 

 rye-grass, germinate at temperatures between 1° and 5°; French beans, sainfoin, 

 millet, maize, sunflowers, at temperatures between 5° and 11°; tomato, tobacco, and 

 gourds at temperatures between 11° and 16°; cucumbers, melons, and cocoa beans 

 not until above 16°. That is to say, that melon seeds, if placed in damp soil 

 whose temperature lies below 15°, absorb, it is true, the moisture, and swell up, 



