FREEZING OF PLANTS AND ANIMALS. 



99 



Hence we might draw the general conclusion, that all southern 

 plants which are unable to endure our winter have large cells, and 

 that, at the North, only such plants can be naturalized as answer to 

 the requirement of small cells. As in Nature there are no aims, but 

 only necessity, we may also hence conclude that a low temperature is 

 favorable to the development of small cells. We have here, further- 

 more, an explanation of the hairy coats of animals. Animals which 

 live in the North have all a thick coat, while those living in the south 

 have a thin one. The mammoth was covered with hair 12 inches long, 

 while his descendant, the elephant, who lives only in southern climates, 

 is almost naked. Animals coming from the south, and acclimatized in 

 the north, acquire hair, and vice versa. At the poles the fox wears his 

 winter-coat the whole year through. In Sweden his coat remains for 

 10 months ; in Germany, for 6 months ; farther south, 3 months until 

 at last it is entirely dropped. No one will here discover an aim, but 

 rather this necessary consequence, that a lower temperature produces 

 a growth of hair in some way unknown to us. The same is true as to 

 the development of cells. If, as a general rule, a warmer temperature 

 necessitates larger cells, then the plants of southern regions will perish 

 from the frost of northerly latitudes. The leaf of the potato-vine can 

 never endure frost ; but it is only in early spring that the plant can 

 be visited by frost in temperate climates, and there is no frost in sum- 

 mer, while in autumn the tubers ai*e protected by the soil. The young 

 branches of the oak and beech (two trees belonging, indeed, to our 

 climate) are quite as little able to endure the frost, and suffer from it 

 severely during the night in spring. On the other hand, the spicules of 

 the pine and the sword-shaped leaves of the yucca stand the severest 

 cold of our winters. 



As regards the temperature of those portions of plants (sprouts of 

 vines, potatoes, etc.) which are killed by the spring frosts, we have no 

 definite knowledge. It is probable that these parts become, by radia- 

 tion, considerably colder than the shining bulb of the thermometer, 

 and that they do not share in the temperature of the air, but fall to a 

 lower temperature by radiation. In cloudy nights, when the ther- 

 mometer shows 30 or 31 Fahr., nothing freezes, though the contrary 

 takes place on bright nights. But here, too, the smallness of the cells 

 appears to lower the freezing-point of water some few degrees. 



Yet, in thus bringing into very probable relation two different 

 facts, viz., the non-congelation of pupa? and leaves, and the fluidity of 

 molten sulphur and of mist-particles, we have no complete explanation 

 of the phenomenon. Such an explanation would show why it is that 

 small particles have a different freezing-point from large ones of the 

 same substance. This would require a very profound acquaintance 

 with the nature of the molecular motion of heat, as also of chemical 

 affinitv. Gaea. 



