ADAPTIVE VARIATIONS. 375 



istic of alpine plants, viz. : very short aerial stems, with 

 hairy and dark green leaves, and compact inflorescence. 

 Seeds gathered from these plants and sown in Paris 

 after three years produced elongated stems, with less 

 hairy and brighter green leaves, or plants very similar 

 to those from seeds obtained in the neighbourhood of 

 Paris. 



In addition to changes of climate and soil, plants can 

 adapt themselves also to mechanical stresses and 

 strains. Thus Ray * sowed a mould (Sterigmatocystis) 

 in two vessels, one of which was fixed, and the other 

 subjected for two months to a rapid oscillatory move- 

 ment. Instead of a thick feltwork of mycelium, this 

 latter vessel contained small, perfectly spherical, elas- 

 tic masses consisting of entangled filaments. The sup- 

 porting tissues of the plant were strengthened in re- 

 sponse to the violent mechanical strains, the mem- 

 branes being twice or three times as thick, and the fila- 

 ments having many more partition walls. Again, R. 

 Hegler f found that " the hypocotyl of a seedling sun- 

 flower, which would have been ruptured by a weight of 

 160 gm., bore a weight of 250 gm. after having been 

 subjected for two days to a strain of a weight of 150 

 gm. The weight was subsequently increased to 400 

 gm. without injury. . . Leaf stalks of Helleborus 

 niger, which broke with a weight of 400 gm., were able 

 to resist one of 35 kgm. after having been subjected to 

 a strain for about five days." Thus protoplasm has the 

 power of responding to, and counteracting the action 



*C. R. Acad. Sci., cxxiii. p. 907. 



fBer. Verkandl. K. Sachs. Gesell. Wiss., v. p. 638, 1892 (quoted 

 from Heuslow's " Origin of Plant Structures," p. 204). 



