304 Cal'ses and Course of Organic Evolution 



and may have evolved — on the plan of Traube's cells — from 

 complex colloid substances that were energized by combined 

 thermic, lumic, electric, and evolving biotic energies amid 

 the abundant thermal springs of the archiean age. As they 

 spread into cooler areas during succeeding ages, new species 

 must have arisen, many in turn must have become extinct, 

 and some must have migrated into the sea. Such would ex- 

 actly explain present-day conditions. 



The only group of plants that seems closely related to the 

 Cyanophycese is that of the Bacteriaceae. For between some 

 of the paler "bacteroid" unicellular Cyanophyceae and the 

 rod-shaped bacteria the morphological resemblance has often 

 been insisted on; while between the paler, smaller, and multi- 

 cellular thread species of Cyanophyceae and some of the tliio- 

 bacterial and "Beggiatoa" types of bacteria the same is true. 



Of living bacteria about 31 genera and 600 species have 

 been recorded as taxonomically distinct fresh-water or land 

 examples — including saprophytic and parasitic types — while 

 4 genera and about 50 species are marine. The relative pro- 

 portions, here again, strongly indicate a fresh-water origin 

 for the group, while their morphological derivation, as allo- 

 trophic or heterotrophic feeders, from the autotrophic series 

 of the Cyanophyceae, seems strongly suggested. But the 

 probable origin even of the Cyanophyceae from colorless types 

 resembling the autotrophic sulphur and iron bacteria should 

 ever be kept in view, and has already been explained (p. 4*2). 

 Yj\en more markedly amongst the bacteria than the Cyano- 

 phyceae, we note the occurrence of numerous "thermophilic" 

 species, the existence of which has only been revealed fully 

 during the past decade. The condensed account of them 

 given by Ambroz (111:257) sets forth well their biological 

 activities. Setchell (37: 934) has sho\\'n that certain of these 

 can live at 89° C, while we know that spores of some will sur- 

 vive to 100° C. for a considerable period. 



Many and often conflicting views have been expressed during 

 recent years as to the phylogeny of the higher algae. Refer- 

 ence will be made to this below. But tlie subjoined table 



