470 ' LICHENES. 



Phylum 4. THALLOPHYTA. 



This phylum includes many thousand species of simple organi- 

 zation, grouped in many genera and families. The plants compos- 

 ing it have scarcely any woody tissue, and are propagated either by 

 spores or by vegetative division. Most of them are small, but there 

 are some large and conspicuous types in all the classes. 



Terrestrial, saxicolous, or corticicolous plants, composed of filaments without chloro- 

 phyll and of cells containing chlorophyll. Class 1. Lichenes. 



Terrestrial or corticicolous plants, or microscopic aquatics, 



wholly without chlorophyll. Class 2, Fungi. 



Aquatic plants, or microscopic terrestrial or corticicolous organ- 

 isms with chlorophyll. Class 3. Algae. 



Class 1. LICHENES. 



Lichens. 

 Contributed by Lincoln W. Riddle. 



INTRODUCTION. 



Lichens vary so much in appearance and in structure that it is diffi- 

 cult to formulate in non-technical terms any precise statement of their 

 characters. In general, they have a plant-body, known as a thallus, which 

 may appear merely as a discoloration on the bark or rock, or as an irregu- 

 lar, and variously divided membrane, separable from the substratum, or 

 as a tufted growth with erect or pendent branches. The color of this 

 thallus varies as much as the structure: gray, gray-green, whitish or 

 brownish, being the commonest, but orange, red, and black, also occurring. 

 But with all their variety, lichens never have an axis and leaves, and are 

 never grass-gTeen. 



Investigations have shown that this lichen-thallus is actually formed 

 by a fungus growing in association with an alga, the association usually 

 being so intimate and the resulting structure so definite that it appears to 

 be an independent type of plant. On this thallus are borne fruiting-bodies, 

 in the form either of minute closed flasks ( perithecia ) , or, more commonly, 

 as open disk-like or cup-shaped apothecia. 



Lichens may grow on rocks, on the ground, or on the branches or 

 trunks of trees. Oftentimes they grow on bare surfaces that will not 

 support any other form of plant-life. 



Our knowledge of the lichens of Bermuda is based upon three sets of 

 collections. The first was made by H. N. Moseley in connection with the 

 Challenger Expedition in 1872. A list of these lichens, 25 in number, was 

 published by Crombie in the Journal of the Linnaean Society of London 

 for 1877. In 1880 and again in 1881, Professor W. G. Farlow, of Harvard 



