80 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



with Falmellew, than with higher forms. It is possibly, after 

 all, a mere matter of analogy, though some will insist that true 

 species of Nostoc are capable of being develoj)ed into Lichens. 



Fig. 21. 



Hormosiphon arcticus, Berk. 



a. Plant, natural size. 



h. Portion of do., magnified. 



c. Thread of spores, with its gelatinous envelope. 



From a specimen gathered near Beechy Island, by Dr. Sutherland. 



63. A point, however, of considerable imj)ortance is this : 

 that, both in Algee and Fungi, there is a complete series of 

 forms from beings of extreme simplicity of structure, consisting 

 of merely one or two cells from which more complicated 

 organisms gradually diverge, ending in the most perfect Sea- 

 weeds and Fimgi ; while in Lichens, the very simplest display 

 perfect fruit, resembling altogether that of Fungi, insomuch 

 that, of many species belonging to either group, it is almost 

 impossible, in the absence of crust, to say whether we have a 

 Lichen or a Fungus before us. It seems, therefore, far prefer- 

 able, to regard Lichens as forming a great group, co-ordinate 

 with Fungi, but of an inferior dignity to the parent group, or 

 to Algae. The only acute difference that can be pointed out be- 

 tween Fungi and Lichens, is the presence of green bodies, 

 called gonidia, in the latter (reproductive bodies produced 

 from the tips of certain internal threads), and this even ceases in 

 some of the more obscure Verrucariw, and in epiphyllous spe- 

 cies. It is impossible, in fact, to point out any real difference 

 between Asterina, and such species of Strigula as S. Bahing- 

 ionii, and it must be remembered, that Fungi, with a similar 

 habit, take their first growth, like Strigula, beneath the true 



