ii2 ALFRED IF. BENNETT [august 



in many ways. In some the leaves are thick and fleshy, as in species 

 of Sempervivum, Pinguicula, etc. ; or they are crowded together in 

 dense rosettes, as in so many members of the orders Cruciferae or 

 Caryophyllaceae. Others are covered with a dense felt of hairs, as in 

 species of Achillea, Artemisia, or Gnaphalium, including the Edelweiss. 

 In others again protection is afforded by the rolling back of the 

 margin of the leaf, as in Azalea procambens, JSmjpetrum nigrum, etc. 

 The greater rarity of the air at high altitudes implies, of course, a 

 smaller supply of carbonic acid gas from which to build up the food- 

 materials of the plant. Hence the organs in which alone this manu- 

 facture of food-materials can take place, the green leaves, are almost 

 invariably strongly developed. 



In a very interesting series of experiments carried on by Prof. G. 

 Bonnier in his experiment-station at Fontainebleau, 1 he appears to 

 have established the fact that it is possible to produce artificially the 

 special characters of alpine plants grown in the open air, by subject- 

 ing lowland species to alternations of temperature comparable to those 

 to which plants are subject at high altitudes. He took a number of 

 familiar lowland plants, — Trifolium repens, Teucrium scorodonia, Senecio 

 jacobaea, Vicia saliva, Avena saliva, Hordeum vidgare, — and, choosing 

 in all cases specimens springing from the same stock, grew them in 

 three sets : the first set was kept continually at a low temperature — 

 4°-9° C. ; the second was grown under the normal variations of 

 temperature in Central France ; while the third set was subjected to 

 very low night temperatures, and to strong insolation during the day- 

 time. As a rule he found that in the third set the subterranean parts 

 of the plant became more developed relatively to the aerial stems ; the 

 latter became shorter from an abbreviation of the internodes, more pro- 

 cumbent, and either more woody or more hairy; the leaves were 

 smaller, more fleshy or more hairy ; the flowers were produced at an 

 earlier period, and were relatively or even actually larger, and were 

 more brightly coloured. The internal structure of the leaf showed 

 corresponding changes : — the epiderm was less strongly cuticularised ; 

 the palisade-tissue became relatively more important ; and, in the 

 same leaf-area, the function of chlorophyllous assimilation became 

 more intense. If, as would appear from these experiments, the 

 anatomical and morphological characters of alpine plants are the 

 direct outcome of a response to external conditions, and if these 

 characters are perpetuated from generation to generation, this would 

 seem to afford strong evidence of the non-universality of Weismann's 

 law, that acquired characters cannot be transmitted by heredity. 



The number of species of which the flora of the Alps is composed 

 varies, of course, with the view entertained by the botanist of specific 

 limits. The late Mr. John Ball, president of the Alpine Club, the 



1 Ann. Sci. Nat. (Botanique), vol. xx. 1895, p. 217 ; Canutes Lendus Acad. Sci. Paris, 

 vol. cxxvii. 189S, p. 307. 



