400 THE POPULAR SCIENCE MONTHLY. 



atmosphere escapes through, special openings in the epidermis, 

 which are called stomata, or breathing pores. These openings 

 are not visible to the naked eye. Fifty of these stomata may be 

 counted on a square millimetre of leaf surface, and the number 

 sometimes rises to five hundred in the same area. Each leaf is 

 therefore provided with several million such openings. They ex- 

 pand or contract according to the necessity, and the correlation 

 is so well adapted that the width of the opening is regulated so as 

 to agree exactly with the existing conditions. They are usually 

 closed at night, when a strong evaporation is not called for, be- 

 cause the salts which the water carries into the leaf can only be 

 elaborated in the light. The transpiration being diminished at 

 night, besides, by the lower temperature and the increased moist- 

 ure in the air, the stomata can often remain open at that time 

 without injury. This would be the case, for example, when the 

 breathing process which is likewise carried on through the 

 stomata is prolonged. The effect of the light is to open the 

 breathing pores at dawn if they are closed, or to expand them. 

 An increase in transpiration is now wanted, and it facilitates the 

 exchange of gases by the assimilation of carbon. The opening 

 fails to respond to the stimulus of the light if there is not enough 

 water for the demands of the plant, when rapid evaporation 

 would promote wilting. The active mechanisms of the plant 

 react upon the external influences, and are in turn affected by 

 them in the manner most advantageous to the plant at the given 

 moment. The fact that the plant is not able to choose its reac- 

 tions freely causes these reactions always to occur correctly ac- 

 cording to the course of the external conditions. Translated for 

 Tlie Popular Science Monthly from the Deutsche Rundschau. 



The Flora Italiana^ begun in 1848 by Filippo Parlatore, and now completed 

 except as to a part of its seventh volume, is, according to Garden and Forest, one 

 of the few floras of large countries or of extensive botanical regions that have 

 come so near their end. The two others of note are Bentham's Flora of Aus- 

 tralia and Boissier's Flora of the Orient. The other great floras, including Gray's 

 of North America and Sir Joseph Hooker's of British India, are still unfinished. 

 Notwithstanding the much that has been achieved in learning the characters, 

 relationships, uses, and distribution of plants, our knowledge of them is still frag- 

 mentary and often unsatisfactory, and a vast amount of woi'k remains yet to be 

 done by morphological and economic botanists. 



"BucKLAND is persecuted," wrote Baron Bunsen of the eminent geologist to 

 his wife in April, 1839, "by bigots for having asserted that among the fossils 

 there may be a pre-Adamite species. ' How,' say they, ' is not that direct, open 

 infidelity? Did not death come into the world by Adam's sin? ' I suppose, then, 

 that the lions known to Adam were originally destined to roar throughout 

 eternity I " 



