LICHENS. 



the term hypothallus is applied, and which constitutes the 

 vegetative system of the future lichen. So far the develop- 

 ment is the same as that of the fungi ; but at a longer or 

 shorter period after the formation of the hypothallus, wo 

 may observe upon its surface a whitish layer of spheroidal- 

 cellules, intimately united with each other as well as with? 

 the filaments from which they take their origin. This 1 

 layer is the groundwork for a second formation of globular 

 cells, and these are only to be distinguished from the 

 first by the chlorophyll which they contain. They are- 

 called gonidia, and are peculiar to Lichens. Such is the 

 formation of the most simply organized of the class, as the 

 Verrucarice, the receptacles (apothecia) of which closely 

 resemble those of a SpJiceria, and are found npon the sur- 

 face of the hypothallus. In the more complicated foliaceous 

 Lichens,as Parinelia^ihe mature thall us is made up of two< 

 kinds of tissues, the medullary and corticated. The cor- 

 ticular portion forms the layers, an inferior and superior, 

 and consists of thick-walled cells, closely adherent to 

 each other ; from the surface of the inferior layer are given 

 off numerous root-like appendages, on either side of which^ 

 or rather embedded in its cortical substance, are the gonidia^ 

 which form a green tissue. Of the spore-like organs^ 

 spermatia and stylospores, there are three varieties, to 

 which the terms apothecia, spermogonia, and pyenides 

 have been applied. The most common form of the apo^ 

 thecium is that of the disc, which may be plane, convex,, 

 or cup-shaped. This form is that which characterises the- 

 Gymnocarpous Lichens. In the Angiocarpece the organ is 

 closed upwards, its superior surface becoming internal, s*> 

 as to form a conceptacle like that of the Pyrenomy- 

 oetes ; the form, however, of which is subject to mucK- 

 variation. 



The reproductive organs of Lichens, as in Fungi, are of 4 

 five kinds . 1, Sporules, which are formed by the con- 

 struction and subsequent separation of the extremity of a* 

 simple cylindrical filament ; 2, Spermatia with their sup* 

 porting pedicles ; 3, Stylospores with their styles ; 4 y 

 Theca? or asci ; 5, Basidia with their basidiospores. As 

 regards the complexity of their form and structure they, 

 may be taken in the order in which they are here placecV; 



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