AS COMPARED WITH THAT OF THE PRESENT DAY. 



413 



* 



value to some dozen, or more, of such isolated fragments as would 

 alone be found. Further instances of variation of form in the same 

 plant are given at Figs. 1 and 6 of the illustrative wood-cuts. 



On the whole, it is probable that the irregularity of outline and 

 division, prevalent in recent ferns, is the most fertile source of error 

 in our investigations amongst the fossil, because the individual fronds 

 are universally detached, and are seldom seen entire, so that we are 

 ignorant to what portion of the plant the fragments belong. The 

 result is of course the multiplication of species to a degree only com- 

 mensurate with the protean nature of the species. 



