270 PLANT MORPHOLOGY 



leaf. Generally the root arises first and grows considerably before the 

 other organs are differentiated. The leaf is the last member to appear. 

 Summary. The Ophioglossales are homosporous and eusporangiate. 

 The sporangia are borne on a characteristic "fertile spike," which prob- 

 ably represents a single leaflet in Helminthostachys and two united basal 

 leaflets in Ophioglossian and Botrychium. The sporangium wall is several 

 layers of cells thick and is without an annulus. The leaves are erect in 

 vernation, not circinate. The gametophyte is subterranean, saprophytic, 

 and without chlorophyll. It contains an endophytic fungus. The 

 antheridium develops as in the other eusporangiate pteridophytes. The 

 inner portion of the embryo forms the foot, the outer portion the root, 

 stem, and leaf. The Ophioglossales have a number of distinctive fea- 

 tures. The vegetative structure of the sporophyte is advanced, but the 

 spore-producing structures and the gametophyte are primitive. The 

 order may have been derived from the Coenopteridales, but does not seem 

 to have given rise to any other modern group. 



3. Marattiales 



The Marattiales are an ancient order of ferns extending back into the 

 Paleozoic. In certain respects they are intermediate between the Ophio- 

 glossales and Filicales. Although once widespread and abundant, they 

 are represented today by only 7 genera and about 55 species almost 

 exclusively tropical in distribution. The largest genus is Angiopteris, 

 with 25 species. It is found only in the Eastern Hemisphere. Two other 

 important genera, each with about 13 species, are Marattia, occurring in 

 tropical regions throughout the world, and Danaea, confined to tropical 

 America. The four other genera, each with a single species, are confined 

 to southern Asia. 



Sporophyte. The Marattiales are mostly large ferns with thick fleshy 

 leaves (Fig. 226). In most species of Danaea the stem is creeping and 

 occasionally branched, but in nearly all other members of the order it is 

 short, stout, erect, and unbranched. The stem is always covered with 

 persistent leaf bases. The roots are thick and fleshy and the leaves, 

 which in Angiopteris may exceed 5 m. in length, are in nearly all cases 

 pinnately divided. A peculiarity of the group is the occurrence of a pair 

 of fleshy stipules at the base of each leaf. The venation is dichotomous 

 and open except in one genus (Christensenia) , where it is reticulate. The 

 vernation is circinate throughout the order. Elongation of the root and 

 stem takes place by means of a meristem, an apical cell being present only 

 in young plants. In possessing an apical meristem, the Marattiales differ 

 from all other ferns. 



Vascular Anatomy. A cross section through a leaf reveals an epidermis 

 on both surfaces, with stomata present only below. Palisade tissue is 



