THE OLDER SPOROPHYTE 175 



At a later stage, probably about the time that the seventh leaf is formed, there 

 arises the single axial (commissural) strand, which is cauline in its origin and which, 

 as Brebner has stated for D. simplicifolia, is the only strictly cauline portion of the 

 vascular system of the stem. This can first be seen at about the same time that the 

 first double leaf trace appears. 



The development of the vascular system was not traced further, as it has already 

 been adequately described by Kiihn (Kiihn 2), and except for the increased number 

 of leaf trace and commissural strands the vascular system is essentially the same 

 in a young plant Hke that shown in fig. 157 as it is in the adult sporophyte. 



Brebner's account of the development of the young sporophyte in Dancea 

 simplicifolia agrees essentially with my own studies of D. elliptica, D. jenmani, and 

 D. jamaicensis. He failed, however, to get successful sections of the transition 

 region between the root and the cotyledon, or, as he puts it, "between the root and 

 stem," and his statements that the central bundle begins as a "haplostele," i. e., 

 a protostele, is not borne out by my studies on the other species. Moreover, his 

 statement that "in this way the somewhat irregular adelosiphonic dictyostele of 

 Dancea is established now by a process which is, to all intents and purposes, a 

 branching of the haplostele, due to the departure of the leaf traces of closely set, 

 spirally arranged leaves," might better be stated, "the dictyostele arises by a process 

 which is essentially the fusion of the leaf traces of closely set, not necessarily spirally 

 arranged leaves." He fully recognized the important part which the leaf traces 

 play in the building up of the dictyostele of the stem, but he did not apparently 

 recognize these as the sole factors in the development of the dictyostele of the older 

 stem. He does, however, specifically state that the axial or commissural strand is 

 the only part of the vascular system which is strictly of cauline origin. 



THE ADULT SPOROPHYTE OF DANiEA. 



The anatomy of what was supposed to be the sporophyte of Dancea was first 

 described by Holle (Holle 2), but the later investigations of Kiihn showed that the 

 plant investigated by Holle could not have been a Dancea, nor could it even have 

 belonged to the Marattiaceas, since Holle describes the rhizome as developing a 

 sheath of sclerenchyma, a condition of things which has not been found to exist 

 in any Marattiaceae. Kiihn's account is very far from complete and the description 

 of the sporophyte given by Brebner (Brebner 3) fori), simplicifolia does not deal 

 with the adult sporophyte. The account given here is based mainly upon a study 

 of D. jamaicensis and D. elliptica, but an investigation of certain points was also 

 made in D. jenmani . The rhizome in D. jamaicensis and D. jenmani is a markedly 

 dorsiventral one. These two species are a good deal alike, but are readily dis- 

 tinguished by the difference in the form of the leaves. In the former the leaves are 

 rather larger and have more numerous pinnae, while the terminal pinna is developed. 

 D. jenmani has somewhat smaller leaves with from seven to nine pairs of leaflets, 

 and the leaves are abruptly pinnate, the terminal pinna not being developed (plate 9, 

 A, fig. I). 



The leaves are arranged very much as they are in Helminthostachys or in 

 Ophioglossum pendulum, the fleshy leaf base being provided with two very conspic- 

 uous stipules which are developed very early in the life of the sporophyte. The 

 exact number of roots corresponding to a leaf is not easy to make out, but there are 

 at least two, and it is quite possible that the number may sometimes be greater. 

 These roots branch freely, especially toward the tips. 



D. elliptica (plate lo) is a good deal larger than the other species and the stout 

 rhizome, which, including the persistent leaf bases, has a diameter of 3 centimeters 



