ELEMENTARY VITAL PHENOMENA 



223 



one side of an elongated structure swells more than the opposite, 

 the former becomes lengthened more than the latter, and the 

 result is a bending of the whole structure, which takes place 

 suddenly or gradually as the swelling is rapid or slow. 



The well-known resurrection-plants (Selaginella lepidophylla), 

 which of late have frequentlj^ come to Europe from the American 

 deserts, are characteristic objects for the observation of swelling- 

 movements. During a drought their leaf-stalks are brought 

 together like the fingers in a closed fist, but when moistened they 

 bend out as in the open hand, the leaf-stalks strongly swelling 



FjG. 88. — Seed of the crane's bill (Erodium cicv tarium), a, in the dry, &, in the swollen state. 



upon their inner side. The well-known rose of Jericho, which 

 is simply the dry, dead branch of a crucifer (Anastatica) 

 growing in the Arabian deserts, behaves similarly. Its spreading 

 when placed in water has led to the common belief that 

 the rose of Jericho is resurrected to a new life, while in reality 

 the phenomenon depends merely upon the swelling-movements of 

 the dead branch. Selaginella, however, is a real resurrection-plant 

 in so far as it can remain for years completely dry without losing 

 its capacity of life. The seeds of many species of crane's bill 

 likewise show very clearly the phenomena of swelling-movements. 

 Erodium ciciUarmm has seeds that are provided with a long stalk 



