160 THE BEGINNINGS OF LIFE. 



and interrupted in their development by the deficiency 

 of water 1 . 



In 'Experiment h the bodies found were of the bright- 

 est green colour, and were almost precisely like repre- 

 sentatives of the genus Scenodesmus^ which is usually 

 included amongst the Pediastreae. But in other experi- 

 ments the organisms seemed more closely to resemble 

 the simple Desmids belonging to the type known as 

 Artkrodesmus^ and some of these exhibited tendencies to 

 grow in a filiform manner. 



The conflicting opinions of naturalists concerning 

 the affinities and degree of relationship existing 

 between Algas., Pediastrese, and Desmids, are sufficient 

 to show the close alliance of these various forms. 

 Pritchard says in his c History of Infusoria ' (p. 30) : 

 c Mr. Ralfs followed Ehrenberg, Meneghini, and others 

 in placing the Pediastreae among Desmidias; but 

 Corda, Nageli, and Braun have separated the two as 

 distinct tribes. Indeed Mr. Ralfs has modified his 

 views since the publication of his monograph, and 

 would treat the Pediastreae as a sub-family of Des- 



1 Professor Lindley writes : ' Pulverulent Lichens are the first plants 

 that clothe the bare rocks of newly-formed islands in the midst of the 

 ocean, foliaceous Lichens follow these, and then Mosses and Liverworts. 

 They are found upon trees, rocks, stones, bricks, pales, and similar 

 places ; and the same species seem to be found in many different parts 

 of the world thus the Lichens of North America differ little from those 

 of Europe. They are met with in one place or other, from the equator 

 to the pole, and from the sea shore to the limits of eternal snow.' 

 (' Vegetable Kingdom,' p. 47.) 



