176 



THE MARATTIALES 



or more, is upright, the leaves being spirally arranged as they are in Marattia and 

 Angiopteris. The petioles in this species are characterized by curious enlargements 

 or nodes, which may occur in the other species also, but are much less prominent. 

 The leaves of D. elliptica reach a length of about 50 centimeters and the leaflets, 

 which are much larger than those in the other species, are less numerous, there being 

 usually about eleven. The conspicuous nodose swellings seen in the petiole are 

 repeated on a smaller scale in the rachis at the base of each pair of leaflets. Sections 

 of the stems were examined in D. jamaicensis and D. elliptica, which, except for a 

 diflFerence in size, agree closely in their structure. The ground tissue, as was first 

 pointed out by Kiihn, consists entirely of parenchyma, through which are scattered 

 many conspicuous tannin sacs which, in preserved material, appear to the naked eye 

 as numerous black specks. The section of the vascular cylinder looks very much 

 like that of the younger sporophytes already described, but the number of bundles 

 seen in the section is larger, and there is a group of several bundles instead of the 

 single medullary strand seen in the section of the younger stem. In a section from 

 a large specimen of D. elliptica in which the rhizome, including the old leaf bases. 



Fig. 160. 



A. Section of petiole of fourtli leaf of Damea jamaicetuis. X40. 



B. Leaf trace. 



C. Bundle of petiole. X180. 



was about 3 centimeters in diameter, the outer ring of bundles contained thirteen, 

 while within this was a smaller circle composed of five medullary bundles, three 

 large ones and two smaller ones. In a similar section of a medium-sized section of 

 D. jamaicensis, in which the rhizome was about half the size of that in D. elliptica, 

 there were nine bundles in the outer ring and four in the middle, two large ones and 

 two small ones. In this section the junction of a root was cut through and the root 

 stele was seen to be applied by its broad base to one of the larger of the medullary 

 bundles (fig. 161, A). 



The relation of this central group of bundles in the stem to the primary medullary 

 strand was not investigated. Brebner has shown that in the later stages of the young 

 sporophyte InD. simplicifolta the original medullary strand — which, as we have seen, 

 is really the only part of the vascular system which is strictly of cauline origin — 

 fuses at certain points with the bundles of the outer ring, and at this point of fusion 

 there may be a branching so that a section above this shows two of these medullary 

 bundles. Whether all of the central group of bundles seen in the stem of the adult 



