PAST HISTORIES OF PLANT FAMILIES 



121 



Though the whole arrangement appears to differ 

 so widely from other stems in the plant world, careful 

 comparison with young stages of recent Cycads has 

 indicated a possible remote connection with that group, 

 while in the primary arrangements of the protosteles a 

 likeness may be traced to the 

 ferns. The roots, even in their 

 primary tissues, were like those 

 of Gymnosperms, but the foliage 

 with its compound leaves was 

 quite fern-like externally. A 

 small part of a leaf is shown in 

 fig. 83, and is clearly like a fern 

 in superficial appearance. The 

 leaves were large, and the leaf 

 bases strong and well supplied 

 with verv numerous branching 



J o 



vascular bundles. 



-a 



Fig. 82. Steles of Medullosa in Cross 

 Section of the Stem 



A, Primary solid wood ; S, surrounding 

 secondary wood. 



Fig. 83. Part of a Leaf of Medul- 

 losa, known as Alethopteris, for long 

 supposed to be a Fern 



The connection between this plant and certain large 

 three-ribbed seeds known as Trigonocarpns is strongly 

 suspected, though actual continuity is not yet established 

 in any of the specimens hitherto discovered. These 

 seeds have been mentioned before (p. 76 and p. 82). 

 They were larger than the other fossil seeds which we 



