AS COMPARED WITH THAT OF THE PRESENT DAY. 



407 



At Fig. 5 again a portion of a fern frond is figured, which, when out 

 of fruit, would be referred indiscriminately to one of four species, differ- 

 ing only in the form, protection, or position of their sori. Thus, at 



Fig. A, the sori are placed on the middle of a venule, and are unpro- 

 vided with an involucre : were the whole frond thus characterized it 

 would be that of Goniopteris crenata. At B the sori are elongated, 

 covering the whole venule ; it is Stenogramma aspidioides. Fig. C 

 shows the sori to be situated at the middle of a vein (as in A), but 

 they are here covered with an involucre, and not exposed ; such is the 

 case with Nephrodium glandulosum. The sori at D again are naked 

 and round (as at A), but instead of being placed in the middle of a 



