126 



ANCIENT PLANTS 



Fig. 86.— Stele of As- 

 terochlaena, showing its 

 deeply lobed nature 



degrees of complexity. There is, unfortunately, but 

 little known as to their external appearance, and almost 

 no definite information about their foliage. They are 

 principally known by the anatomy of their stems and 

 petioles. Some of them had upright 

 trunks like small tree ferns (living tree 

 ferns belong to quite a different family, 

 however), others appear to have had 

 underground stems, and many were 

 slender climbers. 



In their anatomy all the members 

 of the family have monostelic struc- 

 ture (see p. 62). This is noteworthy, 

 for at the present time though a 

 number of genera are monostelic, no 

 family whose members reach any considerable size or 

 steady growth is exclusively monostelic. In the shape 

 of the single stele, there is much variety in the different 

 genera, some having it so deeply lobed that only a care- 

 ful examination enables one 

 to recognize its essentially 

 monostelic nature. In fiof. 

 86 a radiating star-shaped 

 type is illustrated. Be- 

 tween this elaborate type 

 of protostele in Asteroch- 

 laena, and the simple solid 

 circular mass seen in Botry- 

 opteris itself (fig. 88) are 

 all possible gradations of 

 structure. 



In several of the srenera 



o 



the centre of the wood is 

 not entirely solid, but has cells of soft tissue, an incipient 

 pith, mixed with scattered tracheids, as in fig. 87. 



In moj.t of the genera numerous petioles are given 

 off from the main axis, and these are often of a large 

 size compared with it, and may sometimes be thicker 



Fig. 87. — The Stele of a Botryopteridean 

 Stem, showing soft tissue in the centre of the 

 solid wood of the protostele. (Microphoto.) 



