170 MACOUN AND BURGESS ON 



Apart from the foregoing there are variations which cannot always l>e referred to as* 

 certainable causes. Many forms arc found differing from the normal type, yet clearly 

 traceable as only forms of it, and, when these are capable of transmitting their peculiari- 

 ties to subsequent generations, they are styled varieties. In all such cases, however, there 

 is an innate tendency to revert to the original type, and the best systematists endeavour 

 to restrict, as much as possible, the so-called varieties. Notwithstanding this, as it cannot 

 be disputed that the study of forms tends greatly to enlarge our knowledge of the real na- 

 ture of species, and, as this diversity of form often constitutes one of the great barriers to 

 our feeling sure of a specimen being properly placed, while only recording the most de- 

 fined and fully recognized forms as distinct varieties, a fair degree of prominence has been 

 given to those minor deviations on which are based the more questionable ones. 



Though free use has been made of the best works, both American and European, in 

 the preparation of the specific descriptions, these have, in all cases except those of Schizoea 

 pusilta and Phegopteris alpestris, been drawn from Canadian specimens, large numbers of 

 which, from widely separated localities, have been submitted to close examination, and 

 carefully compared with American and often foreign plants. In this connection gratitude 

 for valuable assistance — not alone in material supplied for examination, but also in infor- 

 mation furnished — must be expressed to various friends, of whom Professor D. C. Eaton 

 of New Haven, Conn. ; Professor Lawson and Mr. Peter Jack of Halifax, and Mr. A. H. 

 McKay of Pictou, Nova Scotia; Mr. James Fletcher of Ottawa, Mrs. Eoy of Owen 

 Sound, and Dr. Millmau of London, Ont., have not been the least forward. 



The synonymy has been made full enough to include most of the more familiar names, 

 which have at different times been so lavishly applied to many of the species, and pains 

 have been taken to introduce Canadian references, in order to facilitate future researches 

 into the home history of any of the forms. Where any economic value, in either science 

 or the arts, exists, or has existed, in a species, a note of such has been appended. 



In conclusion of this, perhaps already too lengthy, introduction, and before proceed- 

 ing to the description of the individual species, a few words as to ferns in general and their 

 mode of development may not be out of place. "While in appearance and habit they pre- 

 sent an infinite variety, from the sedge-like Schizoid pusilla to the stately Osmunda regalis, 

 in all, reproduction is carried on through germs (spores), which are almost infinitesimal, 

 dust-like bodies, produced asexually. A spore, unlike an ordinary seed, is not a diminutive 

 plant made up of radicle and plumule, but consists of a little, double-coated cell, differ- 

 ing in shape and external appearance in the different genera of ferns. In germination, 

 the outer layer (exospore) is burst by the absorption of water, and the inner (endospore), 

 which has taken on a process of development by enlargement and cell multiplication, is 

 protruded in the shape of a minute, leaf-like, usually round or heart-shaped, flat patch 

 (prothallium), composed entirely of cellular tissue and quite unlike the parent plant. 

 Among the hair-like root fibres, which, springing from the under surface of the prothal- 

 lium, attach it to the earth, arc now produced a number of other cells, but of two dis- 

 tinct kinds, corresponding to the stamens and pistils of flowering plants, and called 

 antheridia and archegonia. The former are filled with small, ciliate, thread-like bodies 

 (anther ozoids), analagous to pollen, while the latter, which are bottle-shaped, contain an 

 imperfect germ, consisting of a minute, central cell (oosphere). At a certain stage in the 

 process of germination both the antheridia and archegonia burst by the absorption of 



