438 SKETCH OF PALEOBOTANY. 



gams, now chiefly represented by our ferns, club mosses, and scouring 

 rushes. Leaving the cellular Cryptogams undivided, we will consider 

 some of the groups of the vascular Cryptogams. The great preponder- 

 ance of these forms of vegetal life throughout Paleozoic time renders 

 this necessary, notwithstanding their insignificance at the present epoch. 



As in the present, so throughout the past, the vascular Cryptogams 

 are prominently divided into three great groups, which may be roughly 

 designated asthefern group, the Calamite group, and the Lepidodendron 

 group. Ancient ferns differed from those with which we are acquainted 

 in being nearly all arborescent, or tree-ferns. The great Calamites of 

 the coal-measures are now represented solely by our genus Uquisetum, 

 or scouring rush, while the Lepidodendron had degenerated into our 

 little ground-pines and club-mosses (Lycopodium). 



A careful study of the fossil remains of the Calamites and lepido- 

 dendroid growths of the Carboniferous period shows clearly that they 

 were then much more closely related to each other than are the present 

 Equisetaceae and Lycopodiaceae, and there can be little doubt that 

 strictly intermediate forms existed. We may therefore class them 

 together under a larger general group, to which we wiU give the name 

 LepidopJiyies. There is also a suggestive resemblance between some of 

 the tree-ferns and certain of the Calamites, so that far back in that 

 hoary antiquity of vegetable life we find a certain homogeneity and 

 monotony, which show that those plant-forms as we now understand 

 them were to a large extent undifferentiated and blended together. 



Two small orders of cryptogamic vegetation, too rare to be frequent 

 in a fossil state, and, indeed, unless formerly much more robust than 

 now, too frail to admit of preservation except under the most favorable 

 circumstances, possess for the modern cryptogamic systematist an extra- 

 ordinary interest. These are the Ehizocarpese, or pepperworts, now 

 chiefly represented by Salvinia, Marsilia, and Azolla, and the Ligulatse, 

 to which belong only Isoetes, the quillworts, and Selaginella. The reason 

 for this special interest lies in the fact that the plants of these two 

 orders, alone of all Cryptogams, possess characters which seem to mark 

 the transition from the cryptogamic mode of reproduction to that of the 

 Gymnosperms. In this the Ehizocarpeaj are supposed to approach 

 more closely to the Cycadaceae, while the Ligulatse simulate rather the 

 Conifer£e. On account of this exceptional prominence of these two 

 orders I give them a separate place in the following table of classifica- 

 tion of the Cryptogams : 

 Cellular Cryptogams. 



\ Filicine® i ^i^ces (Ferns). 



( -KhizocarpesB. 

 ^ EquisetinesB. 

 Lepidophytte.. ^ Lycopodinese. 

 ( Ligulatse. 

 By uniting this table with the one last examined a somewhat com- 



Vascular Cryptogams. 



