262 THE ANATOMY OF WOODY PLANTS 



opinion now, however, is united in favor of the view that they 

 represent the larger or main roots of lepidodendroid forms. They 

 are, in fact, to some extent comparable to the anomalous roots 

 found in the genus Selaginella known as rhizophores. It seems 

 highly improbable that the type of organization presented by 

 Stigmaria could have belonged to lepidodendrids with protostelic 

 central cylinders. In general, the subterranean organs of plants 

 are less frequently preserved with structural organization, since 



they are from the nature 

 of things less likely to 

 find their resting-place 

 in open bodies of water, 

 and this condition must 

 usually be realized in 

 order to insure petrifac- 

 tion. It is accordingly 

 probable that the genus 

 oc Stigmaria, as at present 

 defined, represents only 

 to a limited extent the 

 main radical organs of 

 lepidodendroid forms. 

 The Lycopodiales as 



FIG. 187. Rootlet of Stigmaria (after Scott) ' r 



a whole are a group 



which reached its culmination in the Paleozoic age and from the 

 richness of its display in earlier geological times must be regarded 

 as extremely ancient. Although the group is almost extinct, its 

 interest from the evolutionary standpoint is great by reason of 

 its antiquity, which supplies valuable data for the elucidation 

 of some of the most important problems of primitive organiza- 

 tion in vascular plants. Clearly the group as a whole displays 

 a reduction series in which the few types which survive under 

 modern conditions represent, not primitive states, but the final 

 results of a process of simplification extending through almost 

 countless ages. Consequently it is highly inadvisable, in attempt- 

 ing to arrive at a conception of the evolutionary significance of 

 the group, to turn exclusive attention to modern simple forms, 



