114 ROCK PLANTS OF THE PASTURES 



two Toadflaxes, the handsome Yellow Toadflax 

 {Linaria vulgaris, Mill) and the Ivy-leaved Toadflax 

 (Z. cymhalaria, Mill), the latter common on old 

 walls. These do not occur within the limits of the 

 Alpine zone. They are there replaced by the Alpine 

 Toadflax, with its violet or deep ultramarine blue 

 flowers, touched with yellow at the throat of the 

 corolla. This plant is thus a further example of an 

 Alpine replacement (see p. 266), and adds another to 

 the large number of the blue-flowered plants of the 

 Alps (p. 43). 



In the Alpine zone this species is usually a 

 perennial. Prof. Bonnier of Paris has experimented 

 with this and other Alpine plants, in respect to its 

 dm'ation of life at diff'erent altitudes. The vast 

 majority of Alpines are perennials, but certain annuals, 

 such as the Snow Gentian {Gentiana nivalis, Linn.), 

 p. 49, and Saxifvaga controversa, Sternberg, p. 82, or 

 biennials such as Campanula thyrsoidea, Linn., p. 90, 

 also manage to flourish very well. Prof. Bonnier 

 finds that many Lowland plants, which are annuals or 

 biennials in the plains, may become perennials if 

 transplanted to the Alpine zone. The Alpine Toad- 

 flax, on the other hand, if removed to the Lowlands, 

 is found to become an annual or biennial. The 

 duration of the life of the individual plant is thus, 

 at least to some extent, adapted to the physical 

 conditions under which it lives. Owing to the 

 shortness of the summer in the high Alps, there is 

 not sufficient time to carry out the life's work in 



