30 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



they must be studied in the herbarium. The practised eye 

 will there detect similitudes between widely different forms 

 which no definition could convey. Now there is certainly much 

 truth in this notion, but more perhaps, from the wrong concep- 

 tion of authors than from the intrinsic difficulty of the case. 

 So long as essential characters are neglected, and fleeting external 

 characters put in their place, difficulty must needs exist, and 

 the student will never be certain that he has come to a correct 

 decision till he has seen an authentic specimen, or compared 

 his own decision with that of other botanists as manifested 

 in extensive herbariums. A state of uncertainty is always 

 one of more or less pain, and the temptation to a solution of 

 the difficulty by the supposition that he has made some new 

 discovery, will often present such attractions as to prove insur- 

 mountable. Nor will he find it possible, without that mental 

 discipline which arises from a patient study of every detail of 

 structure, and of the various shapes which organs may assume 

 under different circumstances. Without such discipline, like 

 certain German authors of some repute amongst persons unin- 

 structed in the subjects they profess to handle, he will propose a 

 new name for every difference, even such as are manifestly merely 

 temporal and accidental, and, on the contrary, he will unite 

 whole groups which belong to entirely different categories. It 

 would be easy to point out glaring examples, both amongst 

 algologists and mycologists. One of the worst amongst Phffi- 

 nogamists, perhaps, is the erection of that state of the inflores- 

 cence of several species of Cissus, in which the peduncles are 

 deformed by the presence of an internal parasite (Puccinia 

 incarcerata, Lev.), into a distinct genus of Phaenogams ; though 

 this is not worse than referring the same Alga received 

 from different sources to two or more distinct genera, and that 

 not among the lower or more obscure species, where there might 

 be some excuse for such a proceeding, or the association of 

 plants so totally different, as Puccinia and Trichothecium. 

 Nor is the correct appreciation of species of so little consequence 

 as is sometimes vainly supposed. The only way in which we 

 can arrive at anything like accurate views of geographic botany, 

 or the distribution of plants over the globe, is by a correct esti- 



