194 



THE MARATTIALES 



even more. The thick, fleshy texture of the leaflets, much like that of Botrychium 

 ternatum or B. silaifolium, at once distinguishes Marattia from any of the large 

 leptosporangiate ferns with which it may be associated. The resemblance to the 

 leaves of Botrychium is especially marked in the young plants growing from the 

 stipular buds. These leaves show a marked triangular outline, curiously similar to 

 that of the larger species oi Botrychium {see. plate 12, B). The venation of the leaf- 

 lets is also very like, resembling that oi Botrychium more than it does that oi Dancea 

 or Angiopteris. In the species with large linear leaflets, e. g., M. fraxinea, the form 

 of the leaf is quite similar to that of Angiopteris or Dancea, but the veins are not so 

 closely approximated. 



The structure of the leaf was particularly studied in M. alata, which closely 

 resembles the Hawaiian M. douglasii. In well-grown specimens the leaves measure 

 2 or 3 meters in length, with a petiole which is 5 or 6 centimeters in diameter above 

 the insertion of the stipules and is somewhat larger lower down. Where it joins 

 the stem there is a marked constriction and the leaves often become broken off at 

 this point, the fleshy leaf base remaining alive and often giving rise to adventitious 

 buds (plate 12, A, 3). A section of the leaf base above the stipules shows the vascular 





Fig. 176. 



A. Sccrion of ultimate rachis of a Icatict of Marattia alata. Tlie shaded area is collencliyma; m, mucilage ducts. 



II. Collcncliyma cells, more highly magnified. 



C. Part of vascular bundle. The shaded cells are tannin sacs. 



bundles to be arranged in two large concentric circles, within which is a smaller 

 third ring corresponding to the two inner bundles found in the section of the younger 

 leaf. Below this point there are numerous anastomoses of the bundles before they 

 enter the cortex of the stem, and the leaf trace consists of a much smaller number 

 of bundles, eight in the specimen examined, which are arranged in a single circle, 

 open on the adaxial side. The distribution of the bundles to the stipules was not 

 studied, but it no doubt corresponds to that in other species, where the veins form 

 an extensively branched system, connected with the bundles of the petiole. 



The large leaves of M. alata, when fully developed, are five-pinnate, the ultimate 

 leaflets being about 2 centimeters long. From the midrib extend lateral veins which 

 usually fork once but may remain undivided (plate 12, A, i). The bundles of the 

 rachis in the later divisions of the leaf diminish in number and show the horseshoe- 

 like arrangement seen in the leaf trace after it leaves the petiole. In the final divisions 

 the crescent of bundles seen in the larger rachis is always completely united and 

 m section appears as a single horseshoe-shaped bundle (fig. 176, A). In the main 

 stipe and secondary and tertiary rachis there is a conspicuous hypodermal sheath 

 of sclerenchyma. This sclerenchyma passes into collenchyma near the base of the 



