Parsons : Flowerless PlxVNts and their Habitats. 35 



The remaining orders of flowerless plants — viz., liciiens, algse, and 

 fungi — belong to the class of Thallogens, which have no distinction 

 bettveen stem and leaves. These orders are hard to define, as they 

 embrace such a large variety of dissimilar forms, and are so closely 

 connected by intermediate links, that the extremes of one order differ 

 much more than some members of the order do from members of 

 another order, and it is therefore very difficult to know where to 

 draw the line. Eoughly speaking, it may be said that lichens are 

 perennial aerial plants, containing green chlorophyll cells, and drawing 

 their nourishment from the air, and not from the substances on which 

 they grow, and which they merely adhere to superficially, and do not 

 penetrate. Alg^e are plants containing chlorophyll, growing in water 

 or on damp surfaces, and drawing their nouiishment from inorganic 

 matters dissolved in water. Fangi are plants without chlorophyll, 

 never aquatic in their perfect fructified state, growing on and pene- 

 trating diseased living, or decaying dead, organic matter, and deriving 

 their nourishment from the substances on which they grow. Chloro- 

 phyll, I may remind you, is the green matter found in plants which 

 has the power, under the influence of light, of decomposing the 

 carbonic acid of the air, and appropriating the carbon to build up 

 into organic matter. 



Lichens vary much in appearance : some are like miniature 

 branching leafless shrubs, others have a flat leaflike frond, and a very 

 large number form merely a crust, closely adhering to the w^ood or 

 stone on which they grow. The fruit consists of knobs or saucer-like 

 shields, generally of a different colour from the rest of the plant. 

 The male element is supposed to be represented by certain little 

 cavities containing minute rodlike bodies, without movement, called 

 spermatia. Besides these organs, lichens bear very generally powdery 

 warts, called soredia ; the grains of whick the powder consists 

 germinate, like the bulbils of mosses, into new plants. Many lichens 

 rarely or never fruit, and are propagated almost wholly by the soredia. 

 Microscopically the frond of a lichen consists externally of a cuticle, 

 or layer of closely-packed colourless cells, beneath this is a layer 

 made up of round green cells, called gonidia, which are the active 

 organs of nutrition; the deeper part of the frond is made up of long 

 interlacing filaments, and beneath all is often a darker layer — the 

 hypothallus. The fruit is made up of elongated sacs called asci, each 

 enclosing one or more spores. Mingled with the asci are a number 

 of slender threads called paraphyses. Arguing from the resemblance 

 on the one hand between the gonidia of lichens and certain single- 



