28 



PAL^ONTOLOGICAL BOTANY. 



which does not increase in height. It produces additions 



Fig. 10. 



laterally, so that the stem increases in thickness. The leaves 



Fig. 10. Asjplenium; a species of Spleen wort. A. Rhizome, r, 

 covered with the bases (stalks or stipes) of the fronds ; /, fronds in 

 bud, rolled up in a circinate manner (this is very rarely seen in fossil 

 ferns) ; g, fronds bearing fructification on their backs. B. Portion of 

 a frond separated to show the linear sori or clusters of sporangia 

 (spore-cases). 



