236 



THE PATH OF DEGENERATIVE EVOLUTION 



Many plants such as Sempervivum 1 (fig. 73) 

 normally possess a very much shortened stem. 

 However, if the plant be grown in a saturated 

 atmosphere the internodes of the stem lengthen out. 



FIG. 73.Sempervivum tectorum. 



A (left figure), normal branch; B (right figure), branch grown for several months in 

 saturated atmosphere. 



Certain Veronicas (fig. 74) bear only small scaly 

 leaves. Cultivation of these plants in an atmosphere 

 saturated with water, results in the appearance of 

 normal leaves. 



Lastly, we may quote again the instances given 

 by Goebel of the production by Equisetum arvense 

 of normal leaves under special conditions. 2 



1 The branch figured here was grown by G. Clautriau, in the 

 Brussels Botanical Institute. 



2 Goebel, Ueber die Fruchtsprosse dcr Equiscten. (Ber. d. d. Bot. 

 Ges.), vol. iv. p. 184, 1886. 



