TRANSACTIONS OF SECTION K. 8-55 



3. On the Anatomy of Danrea and other Marattiacem. 

 By Georgf, Brkbner. 



"\'arious species of the Marattiacepe were studied for the comparative anatomy 

 of tlie adult structure, and Danceci shnpUcifolia, Eudge, for the development of 

 the vascular system. 



1. Development of the vascidar system of Bancea simplicifolia, Eudge. 



The primary vascular axis is a simple concentric stele. The xylem consists of 

 a central mass of small scalariform tracheids, without any conjunctive parenchyma. 

 The phloem consists of a layer of small sieve-tubes separated from the xylem by a 

 layer of parenchyma. The pericycle may be absent or only imperfectly repre- 

 sented. There is a definite endodermis, but the constituent cells are not clearly 

 always the innermost ones of the extrastelar parenchyma. 



When the cotyledon-trace is about to be given oft' the xylem of this vascidar 

 axis, or ' protostele,' is separated into more or less unequal portions by a layer of 

 parenchyma. The parenchyma increa.ses in amount, and ultimately the cotyledon- 

 trace is "separated from the central stele. The cotyledon-trace is collateral. The 

 next few leaf-traces are given otf in the same manner, and are likewise collateral. 

 The stele resumes its simple 'protostelic' appearance. Cauline roots occur, but not 

 regularly. 



vVs further leaf-traces depart from, and root-traces join, the vascular axis, the 

 primitive structure is gradually modified, and it may become more or less 

 crescentic, forming an incomplete, or even complete, gamostelic ring. The spaces 

 left by the departure of the leaf-traces now constitute leaf-gaps. The vascular 

 tissue of this stage may be described as a ' siphonostele with leaf-gaps.' 



The time of appearance of the first mucilage canal varies. The earliest occur, 

 rence noted was after the third leaf-trace had been differentiated. 



In one seedling a curious ligament of phloem was observed, which pursued an 

 oblique course upwards and connected the two horns of a crescentic vascular mass. 

 This strand of phloem interrupted the course of the central mucilage canal. 



At first the leaf-traces are simple and collateral ; later they are simple and 

 concentric ; still later each trace divides into a pair of strands as it recedes from 

 the axis. At a higher level the leaf-trace consists of a pai'- of strands each of 

 which takes its departure separately. 



A remarkable deviation in the early stages of development was shown by one 

 seedling. A mass of parenchyma early made its appearance in the centre of the 

 xylem, simulating a pith. Careful examination showed that this was due to 

 abortion of the cotyledon and its trace, and exceptionally early preparation for thfi 

 departure of the three succeeding leaf-trace^. 



2. Stele of the Marattiacere. 



The structure of the ' stele,' as seen in transverse section, is singularly uniform 

 in essential histological details throughout the group. It may be said to be of the 

 fern type, but there is no endodermis {i.e., in the case of well-grown plants), and 

 tlie pericycle is not characteristically present. 



Tha protoxylem is usually endarch— at any rate in the frond— but it may be 

 mesarch. 



Tlie protophloem is internal. This was first demonstrated in the steles of the 

 stem by Miss Shove.' It has since been found to be internal in the steles of the 

 frond of two species of Bancea and of Marattia alata. There can be little doubt 

 that the internal position of the protophloem is general for the steles of both stem 

 and frond in this group of ferns. 



3. Apical growth. 



All the fresh evidence obtained while studying the seedlings of Bancea 

 simplicifoliu is in favour of an initial group, consisting of a few cells, both in stem 

 and root, 



' Annals Bot., vol. xiv. 1900, p. 497. 



^ K 2 



