266 The Living Plant 



Thus much for heat; at the other end of the thermometric 

 scale more abundant and better marked adaptations are known, 

 for the natural temperatures of the earth do fall plenty low 

 enough to prove fatal to working plant protoplasm. The first of 

 the methods of protection against cold consists in the elimination 

 of water, for while moist and working protoplasm is killed near 

 the freezing-point, the dry substance can endure temperatures of 

 more than 200 Centigrade (over 400 Fahrenheit) below zero 

 without injury, and, by the way, in this condition, can also 

 endure heat even above the boiling point of water. This power 

 of resistance of dry protoplasm against cold and heat is doubt- 

 less due to the fact that the injury resulting therefrom is of a 

 chemical nature, and the chemical changes in living protoplasm 

 proceed only in solution, and solution requires water. 



The protection against cold afforded by dryness explains how 

 seeds, which become very dry, can withstand such low tempera- 

 tures. Winter buds, however, and the other living tissues of 

 plants become only partially dry in winter, and consequently 

 are only partially protected by this method; the remainder of 

 their safety is probably secured by the slight amount of heat 

 released in respiration, which continues all winter, and which 

 is effectively conserved by the non-conducting wrappings 

 provided in the air-holding bark, and the woolly coatings of buds. 



From these reasonably certain adaptations we turn to some 

 others of rather a doubtful sort. The leaflets of many kinds of 

 plants, and the flowers of some others, close together or "sleep" 

 at night; and Darwin, who studied these movements most 

 closely, thought they must form a protection against too great 

 cooling at night. This has been doubted of late, and apparently 

 with reason, but nobody has given as yet any more probable 

 explanation. Again, the red color of the spring vegetation has 

 been thought to provide a kind of mitigation of the effects of cold 

 weather then frequent, in that by a certain power it possesses of 

 converting light into heat, it warms up the parts in the bright 



