PREFACE. 



THE preface, as the last part of an author's work, gives him an opportu- 

 nity to review what he has written, to express his own sense of its merits 

 and defects, and to put it in a true light. It is, then, my wish to introduce 

 the preliminary sketch as valuable only for what it presents of truth of the 

 systems it treats of, and as making no claim to other consideration. I 

 feel too deeply the difficulty and the importance of accurate knowledge, 

 to be willing to venture any opinions of my own on the topics of this paper 

 without hesitation. Such reflections as occurred to me in writing it I 

 have however set down, in the order in which they arose, and the man- 

 ner which then suggested itself. The whole is very imperfect, but it 

 contains what it purports to, and I am unable to devote more time to its 

 adornment. 



What follows is a View, as complete, so far as matter goes, as I can 

 make it, of the present received doctrine of structure and metamorphosis 

 in Lichenes, with such portions of the general history of these plants as 

 seemed appropriate. There is nothing, to my knowledge, in English, 

 which fully presents the views of the modern Swedish and German 

 lichenists, nor are such introductions as that of Fries to his "Licheno- 

 graphia Reformata" fairly appreciable by any but quite advanced and 

 experienced cryptogamists. The whole of this part of the treatise is but 

 a shadowing out of the Friesian method, with such other matter as I 

 could bring together from Meyer, Wallroth, Eschweiler, and Luyken. 



The System, at the end, comprises, it will be seen, a complete conspec- 

 tus of all the European genera, and also a synopsis of the North American 

 species which are satisfactorily known to me. This affords a tolerable 

 view of lichenose (and, to some extent, byssaceous) vegetation in the 

 northern half of North America, but it is, 1 fear, much less complete as 

 respects the southern, except in so far as species and genera are common 

 (which to great extent they undoubtedly are) to botfi districts. In the 

 extreme south, some tropical genera are probably more or less represented, 

 and no doubt numerous species occur, which are not found either at the 

 north or in Europe. The whole number of our species here set down, 

 excluding Byssaceae, is 209, which is about 70 more than the largest and 

 only general American catalogue contains; the species in this last being 

 reckoned according to the principles which are expressed in my own. 

 We have, then, as yet known, 43 species less than Britain, 61 less than 

 Switzerland, 105 less than Sweden, and 111 less than France. In fact, 

 however, it is quite probable that we have many more species than the 

 richest European district, on the whole, if not in all particular genera. 



I will add a single remark, which was meant to have been introduced 

 as a note to a passage of Oken, afterwards left out. His system of mate- 

 rialism is so simple, so old, and so entirely hypothetical, that a naturalist 

 may be pardoned the unwillingness to meddle with it at all. This 1 will 

 do only to notice what follows, especially as it gives me the opportunity 

 to reply in some harmonious words of another, who is less known than, 

 perhaps, he deserves to be. The pertinent question, why, if nature has 



