FLORA OF THE WEST YORKSHIRE HILLS. 267 



1900 ft. — Helianthemum vnlgari\ Viola palustris, Saxifraga tridac- 



tylifes, Carex pilulifera, Molhiia aeriilea, Aira caispitosa. 

 2000 ft. — Linum catharticum^ Oxalis acetosella^ Eriophoruni vagi- 



nafum^ Carex pulicaria. 

 2100 ft. — Alchemilla vulgaris, Euphrasia, Eriophorum angusli- 



folium, Aira ftexuosa. 

 2200 ft. — Drab a verna, Erica tetralix, E. cinerea, Vacciniiwi myr- 



tillus, Blechftu?n. 

 2300 ft. — Chrysosplenium oppositifoHum, Galium saxatik, Luzula 



multiflora, Anthoxanthimi odoratum. 

 2400 ft. — Cerastium triviale, Rumex acetosella, Luzula campesfris, 



Festuca ovina, Nardiis sfricfa, Lycopodium clavatu7?i. 



The descending species have more opportunities for descend- 

 ing to lower levels than have the ascending species to rise to 

 higher levels. Many places, though surrounded by lofty hills, are 

 themselves at a comparatively low elevation^^.^^., Settle Bridge is 

 four hundred and fifty feet, Buckden Bridge seven hundred and 

 thirty-two feet, and Malham Cove six hundred and eighty feet 

 above sea-level. Their flora partakes of the same character, and 

 is composed, in the main, of the same plants as that of the heights 

 around them. Then, again, the streams which are so common in 

 hilly districts are oftenest in flood at the very time of the year 

 when seeds are ripe — ^viz., in summer and autumn. In those 

 seasons the rushing waters carry along with them the mature fruits 

 of the plants, which, under normal conditions, grow in their banks, 

 but which at those periods are wholly or partially submerged. In 

 this manner, seeds from the hills are brought down to lower and 

 warmer tracts, where, if circumstances favour them, they gain a 

 footing and flourish abundantly, as, for example, Saxifraga 

 hypnoides. 



These streams, also, filled with water of a low temperature, 

 have a tendency to chill the air, and the rocks in their immediate 

 vicinity, so that Alpine plants find a degree of cold and moisture 

 approximating to that of their native height, and it is in such 

 situations, where a suitable soil is provided for them, that they 

 descend to their lowest levels. 



But as in the case of the ascending species, it is not cold alone 



