112 ALFRED W. BENNETT [AueusT 
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 Gnaphaliwm, including the Edelweiss. 
In others again protection is afforded by the rolling back of the 
margin of the leaf, as in Azalea procumbens, Empetrum nigrum, ete. 
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,’ 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,—TZvrifoliuwm repens, Teucriwm scorodonia, Senecio 
jacobaea, Vicia sativa, Avena sativa, Hordeum vulgare,—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. Sei. Nat. (Botanique), vol. xx. 1895, p. 217 ; Comptes Rendus Acad. Sct. Paris, 
vol. exxvii. 1898, p. 307. 
