GENERAL REVIEW OF CRYPTOGAMS. 145 



characteristic peculiarities of fructification and develop- 

 mental history. We may note first the more important 

 general features of the three classes. 



The ferns include several thousand species, varying 

 widely among themselves in habits and external features. 

 With leaves of extraordinary variety and beauty ; 

 their texture delicate or coriaceous, or extremely 

 thin and translucent, as in the filmy ferns ; of various 

 habits, creeping, climbing, erect, or tree-like ; growing in 

 every quarter of the globe, and yet exhibiting marked 

 preferences of soil and surroundings; a dominant group 

 in earlier geological time, and still holding a manifest su- 

 premacy among the higher cryptogams, — they present 

 themselves as one of the most varied and attractive, and at 

 the same time most easily studied groups of plants. They 

 are of special interest as widely distributed representatives 

 of the higher flowerless plants, since, like other vascular 

 cryptogams, they exhibit certain developmental features 

 that are wanting or are imperfectly seen in phanerogams.^ 



The horsetails are remnants of a family that once flour- 

 ished luxuriantly, reaching its highest development in the 

 Carboniferous period, when there were several 

 genera, including a number of tree-like species. '^"^° ™°*' 

 At the present time, the class includes only one genus, 

 Equisetum, to which the scouring rush, the common horse- 

 tail, and various other species belong. Their structural 

 peculiarities are so strongly marked that their relationship 

 with other groups would hardly be obvious but for the 

 fact that their cycle of development is essentially identical 



Vol. XV (1890), p. 1 ; On the Eelationships of the Archegoniata, Botani- 

 cal Gazette, Vol. XVI (1891), p. 323. Frequent references to other im- 

 portant literature are given by the author in the papers cited. 



1 Cf. Goebel, Outlines of Classification and Special Morphology, p. 204 

 et seq. See also Atkinson, Biology of Ferns. Macmillan & Co., 1894. 



