6 ROUND THE YEAR 



not frozen is a matter of curious enquiry." I suspect 

 that his little Insects were Diptera, such as Psychoda 

 and Trichocera hiemalis, which had escaped the ex- 

 treme cold by sheltering as pupae in decaying vegetable 

 matter, and only emerged as flies when more genial 

 conditions had returned. 



It is surprising how great a severity of cold can be 

 endured by living plants and animals. Siberian 

 Larches endure a mean January temperature of 

 45 C, falling to a minimum of 60, and rising 

 to a maximum of only 28. Plants have been 

 known to survive after being covered for four years 

 by the advance of a glacier, and abundant vegetation 

 surrounds, and in places overspreads, the great glaciers 

 of Alaska. 1 



Evergreen leaves are probably protected to some 

 extent by unfreezable contents (essential oils, resin, 

 turpentine, benzine, carotin, etc.). The fluids of wood 

 are contained in capillary tubes, and it is well known 

 that under such conditions even pure water will only 

 freeze at a temperature below o C. In the same way 

 the very minuteness of certain Insects may be a means 

 of safety in severe cold. We know little of the fluids 

 of plants in the depth of winter, but it is probable that 

 they are then both more scanty and more concentrated 

 than at other times. 



Animals can be, to all appearance, frozen hard, and 

 yet revive. Ross found in the Arctic regions pupae 

 of Colias, which were hard and brittle, but afterwards 

 yielded Butterflies. Pierret observed the same thing 



1 On the endurance of cold by plants see Seward's Fossil 

 Plants as Tests of Climate, ch. iii. 



