THALLOPHYTA; BRYOPHYTA 937 



Arthrophycus harlani of the Medina, probably a trail ; Dendrophy- 

 ctis triassicus of the Newark sandstone, a rill-mark impression. 



b. Fungi. 



Fungi or mushroom-plants are thallophytes devoid of chloro- 

 phyll, and growing often in the dark. They arise from spores, 

 and the thallus is either unicellular or composed of tubes or cell- 

 filaments (hyphse), which may be branched, and have an apical 

 growth, or, again, they are composed of sheets or tissue-like masses 

 of such filaments, forming a uiyccliiim. True tissue may develop 

 in some cases by cell-division in the larger forms. Two classes are 

 recognized : Phycomycctes, which are alga-like, with unicellular 

 thallus and well-marked sexual organs, and Micom^cctes, or higher 

 fungi, with segmental thallus and sexual reproduction. Some of 

 them (Polyporus, Dsedelia) form resistant, more or less woody, 

 structures growing on dead trees. 



The number of species of Fungi is probably around 20,000, 

 though some have placed it as high as 50,000 or even 150,000. 

 Fossil forms extend back at least to the Carbonic, where they occur 

 as hyphse in fossil wood. Good specimens are also found in amber 

 of Tertiary age. 



c. Lichens. 



The lichens are terrestrial thallophytes, composed of alga; and 

 fungi living together symbiotically. The fungi are generally Asco- 

 mycctes, the higher class of Basidomycetes seldom taking part, 

 while the algfe are either the blue-green algae, Cyanopliycecc or the 

 green algae, Chlorophycac. The same alga can combine with dif- 

 ferent fungi CO form different lichens. The fungal portion always 

 forms the reproductive organs, though the algne may do so when 

 separated from the association, and growing free. Reproduction 

 is also carried on by fragmentation. ;'. c, the breaking off of parts 

 capable of starting new plants. There are some thousands of 

 existing species, but fossil forms have not been recognized except 

 from very recent formations. It is not unlikely, however, that 

 lichenous plants formed a chief element of the ancient land vegeta- 

 tion. 



Phylum III — Bryopiiyta. The Bryophyta include the mosses 

 and liverworts, both terrestrial plants. In the former, and in some 

 of the latter as well, the plant consists of a stem bearing small 

 leaves, though in many liverworts this distinction is not i)resent, 



