THE LEWIS BKOOKS MUSEUM. 39 



increased sufficiently in amount and diversity of feature to 

 permit the appearance of land plants, for none, as yet, have 

 been found. It is very probable, however, that they did 

 exist, for they make their appearance in the next succeeding 

 formation, the lower part of the middle Silurian with forms 

 of pretty high type, the ferns. 



A great interval separates land plants from sea weeds. 

 The uniform conditions which prevail in the waters of the 

 sea do not call for that complexity of form in sea weeds 

 which would be required to endure and withstand the vari- 

 ous forces which act on the inhabitants of the land. Hence 

 we find that land plants are more complex and highly organ- 

 ized than sea weeds. 



When the waters were drained off some sea weeds 

 might survive in bogs and marshes, and if they could ac- 

 commodate themselves to their changed circumstances, per- 

 haps they might endure for long periods with a changed 

 character. Still we know nothing of the forms or manner 

 of appearance of the first land plants. The oldest known 

 land plants come from the middle Silurian of Europe, and 

 are represented by a fern, the Eopteris Morieri, a plant of 

 pretty high type. 



It is a singular fact that the family of ferns, though the 

 oldest known land form, is still abundant both in species- 

 and individuals. 



Many types of the older land vegetation, which were 

 introduced long after them, have entirely passed away. 

 This oldest fern does not differ greatly from the modern 

 ones, though the genus and species do not now exist. This 

 fact certainly shows an extraordinary persistence in the 

 fern type, and adds greatly to the interest of this remarka- 

 ble group of plants. Land plants belonging to several dis- 

 tinct types have been found in the upper part of the lower 

 Silurian of Ohio. This horizon in the American column is 

 perhaps but little higher than the habitat of the Eopteris 

 above mentioned, and thus land plants make their appear- 



