FREEZlXti AND DUUNING. 



551 



ateinia geoides) maintain themselves beueath it, unfrozen, even in very severe 

 winters. 



Other plants, again, appear to bo protected against extreme cold bj' the fact 

 that they retire underground during the winter. Large numbers of bulbous and 

 tuberous plants manufacture organic compounds in their green leaves in the warm 

 sunbeams of summer, at once transmitting them below to their subterranean 

 portions. There, thick stems and tubers, ileshy scale-like leaves, and the rudi- 

 ments of new foliage and flowers (which, however, do not appear above-ground 



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Fig. 130.— DoUulimcnt of Bpecial 6liu»ts u( Pulaniuncluii, cnspus, (or hibernation umlcr luitor. 



the same year) are produced from tlie materials supplied. Throughout the winter 

 these structures remain buried in the earth, and are there protected against 

 excessive cold, just like roots. After the winter is over, the flower-stalks and 

 foliage-leaves, commenced in the previous year, rise up in order to bloom and 

 fructify, and to form anew, in the sunlight, organic materials for the subten-anean 

 bulbs, tubers, and root-stocks. It is very interesting to notice that bulbs and tubers 

 bury them.selves deeper in the earth the more exposed their habitat to radiation 

 and cooling, the more they are threatened with the danger that the earth will be 

 covered by only a thin mantle of snow. While, for example, the bulbs and tubers of 

 Gagea lutea and Corydalis cava, when growing in the black humus of beech forests 

 under withered foliage, lie only a few centimetres below the surface, in open 



