PELAGIC PLANT LIFE 



143 



the shores of Iceland, they commence to develop at a great 

 rate, with the result that the plankton in those parts frequently 

 yields abundant though monotonously uniform samples of these 

 degenerate forms. The altered conditions of existence, which 

 obviously must have supervened, have thus resulted in an 

 extensive production of algse, though without investing them 

 with their normal robust appearance. The strings of cells 

 are of much smaller diameter than usual, so that the formation 

 of auxospores cannot have taken place at the stage that is ^^^^^^^^^ 

 usual elsewhere. Wesenberg-Lund has told us that pelagic Lund. 



Fig. 244. 

 la, ChcBtoceras laciniosum : ifi, forma pela^ica ; 2a, C. schiittii : zb, forma oceanica. 



fresh - water diatoms, such as Asterionella gj'-acillinia and 

 Fragilaria crotonensis, keep on reducing their dimensions in 

 the Danish lakes for months, sometimes even for over a 

 year, and then suddenly return to their maximum measure- 

 ments, and that this is undoubtedly due to the formation of 

 auxospores. All are not, however, affected alike by such a 

 change, and the species occur thereafter in two different sizes, 

 making it necessary to express the measurements of their 

 cell-dimensions by means of divergent curves. This goes on 

 uninterruptedly, moreover, and the smallest forms diminish 

 and seem to degenerate more and more, until in Wesenberg- 

 Lund's opinion they lose all power of regaining their normal 



