40 LECTURES ON BIOLOGY 



As soon as the rainy period commences they awaken from their 

 torpor, the mud-shells dissolve in the water, and though at first 

 the fishes appear sleepy and awkward, in a few hours they have 

 regained their natural vivacity. (Fig. 11.) 



The frequently described reviving of the ' Rose of Jericho ' 

 does not fall into this category. There we have to do with a 

 completely dead organism, and the unfolding of the dry branches, 

 the so-called blossoming, is a purely mechanical process due 

 to the swelling of the leaf-stalks. But the Californian Miracle- 

 flower (Selaginella rediviva), which is now frequently seen in 

 Europe, is a ' resurrection plant ' in the truest sense of the 

 word. For months, even years, this pretty plant, shrivelled up 

 into an insignificant greyish ball, may lie about at the bottom 

 of a drawer or on the top of a shelf, but no sooner is it taken 

 out and moistened with water or planted in a flower-pot and well 

 watered, than it unfolds its branches after a few hours, becomes 

 green, and begins to sprout. The instantaneous rise of a vege- 

 tation on the bare, dark rocks of the Cordilleras after a short 

 rainfall, mentioned by many travellers, is due to the sudden re- 

 awakening of Selaginella. 



Some organisms show also an astonishing power of resistance 

 to high and low temperatures. Whilst the protoplasm of the 

 higher animals and plants is highly sensitive to the effects of 

 heat and cold, coagulating at + 50 C. and thereby losing its 

 ability to live, certain of the lower plants, many algae and bacteria, 

 can, without injury, permanently sustain a temperature of more 

 than + 70 C C. Indeed, some of them find there the most 

 favourable conditions of their life. In the water of the Karlsbad 

 Sprudel one may observe numerous filamentous algse (Oscillaria), 

 and in the hot springs of Albano and in the Solfatarra near 

 Naples I observed with astonishment quite a flora of simple 

 plants, and, at a temperature of + 60 C., even minute crustaceans 

 and larvae of insects, all in a flourishing condition. But most 

 astonishing of all is that in the hot springs of Yellowstone Park 

 various species of algae and bacteria thrive at a temperature 

 of + 75 C. 



A still more remarkable power of resistance is observed in 

 bacteria. The spores of many species will sustain without injury 

 being exposed for hours to a heat of 1QO C. Dry spores of 



