108 ACTION OF LIGHT AND HEAT 



fingers frozen. The analogy, however, will go no further, 

 for he has not the advantage of sprouting out new ones. 



And on the other hand, what degree of heat will plants 

 support ? 



Mrs. B. It varies extremely, depending on a variety 

 of circumstances. The Vitex agnus castus has been 

 known to strike root in water at the temperature of 170 

 Fahrenheit. 



When one of the hothouses of the Botanical Garden of 

 Paris was burnt, all the plants within it perished excepting 

 the flax of New Zealand, which resisted the temperature 

 of a general conflagration that consumed even its leaves. 



The temperature of some few plants experiences an 

 elevation at the moment of flowering : that of the Arum 

 maculatum rises from fourteen to twenty one degrees, 

 when its blossom expands between three and five o'clock. 



Emily. Do plants, like unorganized bodies, partake 

 of the temperature of the atmosphere in which they grow? 

 I should have imagined that they must be warmer ; for, 

 since some portion of the water which a plant absorbs 

 remains incorporated in it under a solid form, in chang- 

 ing its state from fluid to solid, it must give out its latent 

 heat, which would raise the temperature of the plant. 



Caroline. But you forget, Emily, that two thirds of 

 the water which the plant absorbs is evaporated, and, by 

 changing its form from liquid to vapor, cold must be pro- 

 duced. Now, as the quantity which assumes the form 

 of vapor is much greater than that which becomes solidi- 

 fied, the temperature of the plant should ultimately be 

 lowered beneath that of the atmosphere in which it lives. 



Mrs. B. Each of your opinions have been sanction- 

 ed by different naturalists ; but, however exact these 

 calculations may be in the laboratory, they can give us but 

 very little insight into the chemistry of vegetation, where 

 that mysterious principle life performs so essential a part. 



Emily. Yet, is it not easy to ascertain by the ther- 

 mometer whether plants differ in temperature from the 

 atmosphere ? 



! 606. At what temperature was the Vitex agnus castus known to 

 strike roof? 607. What is mentioned of the flax of New Zealand! 

 608. What fact is stated of the Arum maculatum! 609. What rea- 

 son does Emily give for supposing that the temperature of plants will be 

 higher than that of the atmosphere in which they growl 610. What 

 reason is given by Caroline for a contrary opinion! 611. What is 

 the reply of Mrs. B. to both! 



