634 STUDIES IN FOSSIL BOTANY 



stature, and organisation, both vegetative and repro- 

 ductive. In spite of their immense development at 

 that time compared with their very subordinate position 

 at the present day, the Lycopods, as a whole, constitute 

 a very homogeneous class of plants, characterised 

 throughout by a microphyllous habit, an anatomy based 

 on an exarch type of protostele, and a simple relation 

 between sporangium and sporophyll. There is no 

 departure from the first- named character ; for though 

 the leaves were often long, they were never large in 

 proportion to the plant, and were always of the simplest 

 form. The double bundle of Sigillariopsis ; a form of 

 leaf belonging to certain species of the somewhat 

 advanced genus Sigillaria, is the only departure from 

 the prevailing simple type of foliar structure (p. 230). 



Attention has already (p. 1 26) been called to the 

 simplicity of the primary anatomical structure of the 

 stem in Palaeozoic Lycopods, the one character in which 

 these plants have proved to be more '' primitive " than 

 most of their recent allies. A gradual transition 

 may be traced from the protostelic type, through the 

 medullated forms of Lepidodendron and the ribbed 

 Sigillarias, to the smooth-barked Sigillarias, in which 

 the ring of wood separates, more or less completely, 

 into distinct bundles (p. 220). It is these last forms 

 which depart most widely from the common Lycopod 

 type, but the change is not a great one, and does not 

 appear to indicate a transition to any form of Gymno- 

 spermous stem. 



As regards the secondary growth, characteristic 

 of the arborescent Lepidodendreae, there are some 

 peculiarities ; the agreement with the normal secondary 



