CYCADOFILICALES 17 



the protoxylem points. The tips of rootlets are not so well preserved ; 

 consequently, it has not yet been determined whether the growth is 

 by a single apical cell, as in the ferns, or by a group of cells; but it is 

 quite possible that there is a single apical cell. 



The cortex of the root is sharply differentiated into two regions, 

 an outer layer two or three cells deep, consisting of thin-walled cells 



Fig. II. — Neuropteris decipiens: from the reconstruction in the Field Museum at 

 Chicago. The photo was taken while the individual plants were being made. The leaves 

 are strongly dimorphic. Most of the seeds (Trigonocarpus) are terminal, but some are 

 lateral. 



with scanty contents and no differentiation in the alternating plates 

 of thick-walled and thin-walled cells which characterize the stem; 

 and an inner cortex, about twice as thick, many of the cells of which 

 show dense contents, which may be largely mucilaginous. 



The microsporangium. — In 1905 Dr. Kidston^'^ discovered im- 

 pressions of Crossotheca in connection with leaves of Sphenopteris 

 hoenighausi, thus proving that Crossotheca is the microsporangium 



