The American Naturalist. 



[.I:m„; 



and examined from time to time for anatomical and physiological 

 changes. These soon made their appearance and were as follows, the 

 changes in the plants exposed to the alpine conditions being attributed 

 principally to (1) More intense light; (2) Drier air ; (3) A lower 

 temperature. Change of form and structure : (1) The subterranean 

 parts as a whole are relatively better developed than the parts above 

 ground. (2) The rhizomes and the roots show little modification, ex- 

 cept that the calibre of the vessels is generally smaller and the bark 

 more precocious ; (3) The serial stems are shorter, more hairy, more 

 spread out, closer to the soil and with shorter and less numerous inter- 

 nodes ; (4) In general the stems have a cortical tissue that is less thick 

 in proportion to the diameter of the central cylinder ; the epidermal 

 cells have thicker walls and the cuticle is more pronounced ; often the 

 epidermis is reinforced by a certain number of sub-epidermal layers ; 

 the different tissues of the central cylinder are ordinarily less differen- 

 tiated ; when bark exists, it appears earlier and is relatively thicker 

 on branches of the same age ; when there are secretory canals, they 

 are relatively, or even absolutely, larger; finally, the stomata are 

 more numerous ; (5) Usually the leaves are smaller, except sometimes 

 in sub-alpine regions, more hairy, thicker in proportion to their sur- 

 face and often absolutely thicker, and deeper green by reflected or 

 transmitted light ; (6) The blade of the leaf acquires 'tissues better 

 suited for assimilation ; the palisade tissue is more strongly developed, 

 either by a narrowing and elongation of its cells or by a considerable 

 increase in the number of rows, the cells also contain a greater number 

 of chlorophyll bodies and often each grain of chlorophyll has a greener 

 tint . when there are secretory canals the diameter is relatively or ab- 

 solutely greater; the epidermis of the leaf shows less differences than 

 that of the stem, nevertheless, in general it is better developed, especi- 

 ally on persistent leaves, which have besides better developed protec- 

 tive sub-epidermal cells ; the cells of the epidermis are ordinarily 

 smaller and often the number of stomata per unit of surface is greater 

 especially on the upper face as M. Wagner was the first to show ; (7) The 

 petiole shows modifications generally analogous to those of the stems 

 but much less pronounced ; (8) The flowers are relatively much larger 

 and sometimes even absolutely larger ; they are more brightly colored 

 and when the color is due to chromoleucites it is the same as in case of 

 the chlorophyll grains, the number in a cell is greater, and often each 

 chromoleucite is of a deeper color; the heightened color occurs also 

 when it is due to substances dissolved in the cell sap. Experiments 

 during eight years with Teucrium also show that modifications acquired 



