398 A TEXTBOOK OF BOTANY [Ch. X 



noted in detail in connection with the alternation of genera- 

 tions thus introduced into the life cycles of these plants. 

 The Thallophytes never produce anything even remotely 

 resembling the flowers and seeds of the higher plants. 



The Thallophytes are disseminated in a great variety of 

 ways, but chiefly by water currents in case of the Algae, 

 and by wind in case of the Fungi. Spores are so small that 

 they float in the air, and penetrate everywhere, with the dust 

 (page 359) ; and since many of the resting spores can endure 

 dryness and heat for months or years, we can easily under- 

 stand how the Fungi, including pathogenic kinds, have 

 become the most ubiquitous of organisms. 



In their relations to man's economic interests, the Algae 

 serve only a few minor uses, but the Fungi are extremely 

 prominent, partly on account of the damage wrought by 

 their parasitism upon crops, and partly because of diseases 

 they cause in man and his domestic animals. The subject 

 has already been treated in brief (page 85), and will receive 

 fuller description in the following pages. 



Both Algae and Fungi fall into groups so related as to 

 imply that the Algae are the more primitive, and the Fungi 

 have been evolved from them through adoption of the 

 parasitic habit, — their chlorophyll, and most of the sexual- 

 ity of their reproduction, becoming lost in the process. In 

 various groups of Algae occur saprophytic and parasitic forms, 

 suggesting the origin of new groups of Fungi ; and many 

 Fungi still show plainly their connections with groups of 

 Algae, though others have lost all external traces thereof, — 

 no doubt because of their very ancient origin and long in- 

 dependent evolution. Parasites and Saprophytes collec- 

 tively are often called hysterophytes. 



The Thallophytes fall into ten classes, which are as fol- 

 lows, the Fungi being arranged opposite the Algae from which 

 they are most probably derived. The student will note 

 the distinction between the terminations -phycece, meaning 

 Algae, and -mycetes, meaning Fungi. 



