SOUTH WESTERN PARTS OF EUROPE. 37 



Acetosella, Oxalis corniculata, Rubus fruticosus, 

 Scirpus setaceus, Aira canescens. 



5. Although some plants peculiar to corn-fields, 

 as Chrysanthemum segetum, Agrostemma Githago, 

 Bromus secalinns, Lolium temulentum, are also 

 indigenous in the South of Europe, yet this is not 

 the case with all. Centaurea Cyanus is often 

 found in the gardens of the most southern parts of 

 Europe, but not in the corn-fields. 



That swamps and stagnant waters produce the 

 same kind of plants under different latitudes, is, I 

 think, the natural consequence of the small differ- 

 ence in the temperatures in which they exist. In 

 the nonhern climates, a covering of ice is their 

 protector during the winter ; in hotter regions 

 they are cooled by the exhalations increased during 

 summer. Hence also it proceeds that the above 

 remark applies only to fwamps and stagnant waters, 

 but does not extend to peat-bogs. These last, 

 being filled up with moss, and freezing to a consi- 

 derable depth, do not permit the roots of the plants 

 to penetrate so deep, which arc therefore more 

 exposed to the action of the frost. 



