﻿TRUNK STRUCTURE. 



53 





Especially in the trunks referred by Profes- 

 sor Ward to Cycadeoidea dacoienszs, C. minnekah- 

 tensis, and C. Marshiana there is a very dense 

 growth of ramentum about the young non- 

 emergent fronds of the summit. The preservation 

 in man}' of these trunks is so perfect that the 

 individual scales preserve their alignment with 

 respect to the young organs beneath, and thus 

 present a series of groups in regular helicoidal 

 arrangement foreshadowing the leaf-base spirals. 

 An example is shown in thin section in photo- 

 graph 5, plate xix. In this instance none of the 

 scales are more than one cell in thickness. 



A hair}- or scaly growth of ramentum, cloth- 

 ing the bases of the fronds, is primarily a feature 

 of filicinean forms, especially those forming 

 trunks. In a few ferns, instead of more scale-like 

 structures, hairs or palea; in the form of single- 

 celled filaments are present; in some other in- 

 stances these are several cells in thickness. In 

 figure 1 6 a single ramentum from the petiole of Cyathea is shown, together with 

 the obviously similar ramenta of Cycadeoidea gigantea from the Purbeck beds of 



Fig. 19. — Cycadeoidea ingens. T. 108." 



Leal bases as naturally eroded or rather broken 

 out of a fragmentary portion o( the armor 

 of a large trunk so as to expose their under 

 surface. One-half natural size. 



Fig. 20. — Cycadeoidea turrita. T. 15. 



Tangential section through armor 2.5 cm. distal to the 

 cortex. Four fructifications are cut. Of these I 

 and IV are well advanced in growth, the section 

 cutting through their seed pedicels. X §• 



Fig. 21. — Cycadella (Cycadeoidea) utopiensis, type. T. 727. 



Tangential section through armor 2 cm. out from the cortex, cut- 

 ting various peduncles, the emergence of which has noticeably 

 disturbed the sequence of the leaf base spirals. X !• 



the Isle of Portland and a single filamentous ramental hair of Dion. The 

 latter is seen to consist in a short, thick-walled stalk cell with a long terminal 

 cell, but is wholly analogous to the more hair-like fern ramenta. Such vestigial, 



* Throughout this volume the cycad trunks and sections of the Yale Museum collection are simply 

 referred to by their catalogue number ; T. denoting the trunks, and S. the sections made from them or 

 from other material. The number following either letter denotes the catalogue number of the trunk or 

 section, as the case may be. 



