PAST HISTORIES OF PLANT FAMILIES 125 



draw accurate conclusions unless the specimens have 

 sporangia attached to them, and this is not often the 

 case. The cuticle of the epidermis or the spores can 

 sometimes be studied under the microscope after special 

 treatment, but on the whole we have very little infor- 

 mation about the later Mesozoic ferns. 



A couple of specimens from the older Mesozoic have 

 been recently described, with well-preserved structure, 

 and they belong to the family of the Osmundas (the so- 

 called ''flowering ferns", because of the appearance of 

 special leaves on which all the sporangia are crowded), 

 and show in the anatomical characters of their stems 

 indications that they may be related to an old group, 

 the Botryopteridecz, in which are the most important of 

 the Palaeozoic ferns. 



In the Palaeozoic rocks there are numerous impres- 

 sions as well as fern petrifactions, but in the majority 

 of cases the connection between the two is not yet 

 established. There were two main series of ferns, 

 which may be classed as belonging to 



I. Marat tiaceae. 

 II. Botryopterideae. 



Of these the former has still living representatives, 

 though the group is small and unimportant compared 

 with what it once was; the latter is entirely extinct, 

 and is chiefly developed in the Carboniferous and suc- 

 ceeding Permian periods. 



The latter group is also the more interesting, for 

 its members show great variety, and series may be 

 made of them which seem to indicate the course taken 

 in the advance towards the Pteridosperm type. For 

 this reason the group will be considered first, while the 

 structure of the Pteridosperms is still fresh in our 

 minds. 



The Botryopterideae formed an extensive and ela- 

 borate family, with its numerous members of different 



