4G 



the species of Plantago, Dipsacus, Echium vulgare, Verbascmn 

 Lychnitis, Thapsus, nigrum, &c., many Syngenisistce and Um- 

 bellifera, species of Lychnis and Potentilla, Fragaria vesca, 

 &c. 



The third class contains partly annuals, which have germi- 

 nated in autumn, but flower in the following spring, and partly 

 perennials, which have developed new branches in autumn. 

 They differ from the plants of the second group, properly 

 speaking, only in this respect, that their leaves form no ro- 

 settes spread out on the soil, but have a longer stem which is 

 covered with leaves in every stage of development. Un- 

 der this section M. Mohl includes a great portion of the 

 grasses, for instance, Bromus mollis, many Euphorbice, Vero- 

 nica, Antirrhinum majus, Cerinthe minor, Senecio vulgaris, 

 Sonchus oleraceus, Hypericum perforatum, &c. The leaves of 

 these plants live very rarely through a whole year. 



The first question M. Mohl endeavours to solve is, whether 

 the red colouring of the leaves in winter is a phenomenon in- 

 dependent of the autumnal colouring of dying leaves, and of 

 the red colouring of leaves in the process of development, or 

 whether it must not rather be ascribed at times to the one, at 

 times to the other of these causes ? A number of plants are 

 enumerated whose leaves are perfectly green in summer, but 

 during winter assume a more or less deep red tint and in sum- 

 mer again become green, which for instance may be observed 

 in various species of Sedum, Sempervivum, and also on the ivy. 

 In the leaves of the second and third divisions we must 

 ascribe the origin of the red colour to the influence of the win- 

 ter cold, as here the leaves in all stages of development take 

 this reddish or brownish tint. As, however, we find, says M. 

 Mohl, on the same plants, leaves which have this red colour 

 in the winter but die in the spring, while other leaves become 

 red-coloured in the same way, and do not die in the spring 

 but again become green and continue to grow, &c., we are 

 justified in denying this connexion between the production of 

 a red colour and the dying off of the leaves, and must admit 

 that the production of the red colour in leaves in autumn and 

 in winter is owing to a change in the physiological functions 

 of the leaves occurring at this season, but that the falling off 

 of the leaves is only accidentally contemporaneous with that 



