RESISTANCE TO COLD. 489 



of one species are content with a low temperature, while those of another require 

 much greater heat, although the eye can distinguish no difference in the structure 

 of their coat, in their manner of storing reserve food, or in the structure of their 

 embryos. The same may be said of the freezing of plants. Many Calif ornian and 

 Mexican Pines (Pinus) are very like those of Northern and Central Europe, and 

 yet the one will be frozen to death as soon as the temperature sinks below freezing 

 point, while the other can sustain winter temperatures of -20 C. without injury. 

 There seems to be no reason why the South European Junipers, Juniperus Oxycedrus 

 and phcenicea, which are apparently of the same structure as the similar species 

 Juniperus nana and Sabina, should not nourish equally well on our mountain 

 heights in the Central Alps, where the latter cover whole mountain peaks and send 

 their roots into ground which is covered with snow eight months every year, and 

 is frozen hard for months together. The common Ivy (Hedera Helix) grows in 

 Central Europe without any protection from the fairly severe cold of winter; the $ 

 European Ivy, Hedera poetarum, which is very similar to the common species, but 

 can be distinguished from it by several external characteristics, requires a protecting 

 roof in the gardens of Central Europe if it is to survive the winter unkilled by t 

 frost The same is true of two closely allied species of Marigold, viz. 

 arvensis and fulgida, the former growing in Central, the latter m Souther 

 Europe In 1874 I sowed seeds of Calendula arvensis from the Rhine 

 side by side in the same garden-bed with seeds of Calendula fulgida, which hac 

 been gathered in Sicily. Very luxuriant plants which flowered in profusion grei 

 up from both kinds of seeds. The first frost in that year in the place where the 

 experiment was made occurred on October 25th. Calendula arvensis was not 

 injured; its foliage was fresh and green, and remained in this condition during t 

 following days, although, until November 2nd, the temperature fell every mg 

 from -?-5 to -? ft, and in the morning the stem, leaves, and flowers were 

 studded with hoar-frost. Calendula fulgida, on the other hand was destroyec 

 the frost on the night of the 24th-25th October. Its leaves and stems withered and 

 LtTLL, and exhibited all the symptoms observable in death by freezing. In 



Mautern, in Lower Aust MP of ^ Q ^ 



apped to be ^ *^JS?*t frost, while'those of the 0**. 



re^ed healthy and'strong. The experhnent was repeated 



without har. Two _ .ater both 



