272 



PLANT MORPHOLOGY 



developed beneath the upper epidermis, the rest of the mesophyll consist- 

 ing of spongy tissue. The roots of the Marattiales are characterized by a 

 hirge numbeitof protoxylem points (Fig. 227). The xylem is usually 

 lignified to the center. 



The vascular anatomy of the stem is very complex. The cortex con- 

 sists of parenchyma containing mucilage canals, but no sclerenchyma is 

 present. The vascular cylinder is a dictyostele with large overlapping 

 leaf gaps and widely separated bundles. The latter, in all genera, are 





Fig. 228. Portion of leaflet of Angiopteris (A) with sori, leaflet of Marattia (B) with oval 

 synangia, and portion of leaflet of Danaea (C) with elongated sunken synangia, X3. 



amphicribral (phloem surrounding the xylem) and either mesarch or 

 endarch in development. In Danaea the vascular bundles are seen, in a 

 cross-sectional view of the stem, to be arranged in a single circle surround- 

 ing the pith. In Marattia the stem is more complex in that two concen- 

 tric circles of bundles are present, while in Angiopteris, where the stem 

 reaches its greatest degree of complexity, there is a series of four or five 

 circles of vascular bundles. In all the Marattiales the stem bundles 

 undergo more or less branching and fusion, and commissural strands, con- 

 necting certain parts of the vascular system with one another, arise inside 

 the dictyostele. Secondary thickening does not occur. As in the higher 

 ferns, the tracheids are scalariform. 



Sporangium. The Marattiales resemble the Ophioglossales in being 

 homosporous and eusporangiate, in having a sporangium wall consisting 

 of several layers of cells, and in lacking an annulus. The sporangia, how- 



