INTRODUCTION TO ORYPTOGAMIC BOTANY. 241 



tant order of plants, which, from the poisonous qualities, the 

 evanescent nature, and the loathsome mass of putrescence 

 presented in decay by many species, have become a byword 

 amongst the vulgar, and are frequently regarded as fit only to 

 be trodden under foot. However such characters may apply 

 to many, there are numerous species which afford a wholesome 

 and sometimes a delicious article of food, and there are others 

 which vie in duration with their close alhes, the Lichens. 

 Indeed, nothing can be more various than the forms which 

 they assume, insomuch that the fleshy mushroom at first sight 

 has little in common with the hard horny Hysterium, and yet, 

 perhaps, no branch of the natural world abounds in nicer 

 transitions, while the groups are often so natural as to make 

 it extremely difficult to assign strictly definitive characters. 

 We are, in fact, frequently obhged to have recourse to mere 

 texture, where no essential differences of intrinsic structure 

 can be found. 



233. From the very notion of a Fungus, as distinguished 

 from AlgEe, it is evident that such a thing as free cells, indefi- 

 nitely increasing the species, without any ulterior development, 

 cannot exist. In aU Fungi there is a portion, consisting 

 either of threads, or more or less closely compacted cells, 

 arising in the first place from the processes put forth by ger- 

 minating spores, and increased by their division and fiurther 

 development, to which the name of mycelium has been given. 

 This may consist of cottony threads of extreme dehcacy, or of 

 closely compacted homy membrane ; but still its office is the 

 same, and it may exist in either form without producing fruit, 

 exactly as a tree may remain barren in a soil or climate which 

 is not congenial. In some cases, as in the substance called 

 Xylostroma giganteum, it forms sheets as thick and dense as 

 leather, destroying wood of the firmest and most solid tissue, 

 without attempting to produce a pileus ; and parallel cases, as 

 in the mycehum of some of the larger SphcsricB, may easily 

 be found amongst the black and ascigerous forms. There can 

 be neither a perfectly free mycelium, nor free organs of repro- 

 duction, except in aquatic or aerial species, which are of very- 

 rare occurrence. Even if floating, there will be something in 

 16 



