Mosses and Lichens 



How it could ever have been young, 



It stands erect and like a stone 

 With lichens it is overgrown." 



Spenser expresses another idea when he saysof the ancient oak : 



"But now the gray moss marred his rine ;" 



and Shakespeare also when he introduces Tamora, Queen of the 

 Goths, to 



" A barren, detested vale . . . 

 The trees, though summer, yet forlorn 

 O'ercome with moss, and baleful mistletoe." 



Titus Andronicus, Act II, Sc, 3- 



Mosses and Lichens are both soil-makers. They work by 

 two methods. The one chemical, the other mechanical. By 

 chemical action they either construct plant tissue of gases taken 

 directly from the air or they first free from rock or wood or earth- 

 mould, the minerals needed and then construct them into plant 

 tissue. By mechanical action they pry off bits of soil from hard 

 rock, arrest dust and debris brought to them by the wind, and 

 constantly add to the mass, such plant tissue as they themselves 

 are continually shedding. 



" Upon this herbless rock a small gray lichen 

 Did fix her home. She came with meek intent, 

 To bless her stern and sterile place of rest ; 

 And presently her gentle sisters followed, 

 Some vestal white , and some in robes of brown, 

 And some in yellow vestures, labouring all 

 At the same work, with tiny cups held out 

 To catch the raindrops, and with mattocks small 

 To pierce the rock. And well did they effect 

 Their destined purpose." 



One of the most important sources of the nourishment of 

 plants is carbon dioxide (C O 2 ). It is the gas which bubbles up 

 from "soda water" and it is the gas breathed out by animals. 

 It is formed wherever a candle, lamp, or wood is burning or 

 wherever vegetable or animal matter is decomposing. The gas 

 is itself a compound of an elementary gas, oxygen (O) united 

 with an elementary solid, carbon (C) known by the common 

 names of charcoal and graphite. Stated in a general way, the 

 carbon dioxide passes through the walls of the plant cells into 

 the cell-contents and there by the leaf-green (chlorophyll) the 



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