THE OLDER SPOROPHYTE 201 



The anatomy of the stem closely resembles that of Marattia, but the bundles 

 seen in section are much more numerous and instead of being arranged in two 

 circles, exclusive of the central commissural strand, are usually arranged in four or 

 five. The first complete study of the arrangement of the bundles in the stem was 

 made by Mettenius (Mettenius 2). A summary of his results is given in the paper 

 by Miss Shove. Briefly stated, Mettenius describes the distribution of the bundles 

 as follows (Shove 1, p. 498): 



"The vascular bundles form funnel-shaped zones, with their lower ends in the 

 axis of the stem and their upper portions continued out into the leaves as leaf traces. 

 It is the transverse sections of these concentrically arranged funnels which appear 

 as the rings of separate bundles in the section of the stem. Segments from the outer 

 zone pass into the leaves as the leaf traces and the gaps thus left are filled up by 

 corresponding segments from the next inner zone." 



The detailed account made by Miss Shove was based upon a moderate-sized 

 specimen from Ceylon. This stem is described as being somewhat dorsiventral in 

 structure, which is certainly not usual in Angiopteris and may perhaps be explained 

 by the conditions under which the plant was growing. I found Angiopteris growing 

 frequently upon steep banks and it is quite possible that plants growing in such a 

 position might be obliged to bend upward, in which case a somewhat dorsiventral 

 structure would be developed. Plants growing upon level ground, so far as my 

 observations go, are always strictly radial in structure. 



Miss Shove found essentially the same structure as that described by Mettenius, 

 except that she states that the leaf traces are developed exclusively from the strands 

 of the outer zone, while Mettenius states that strands are also contributed to the 

 leaf trace from the second zone. The following is taken from her paper (Shove 1): 



"The general scheme of the arrangement of the vascular tissue in Angiopteris 

 is almost clearly conceived by considering it in connection with the insertion of the 

 leaves. The leaf bases, which are set in a rough spiral on the stem, show in their 

 lower parts a meshed segment of vascular tissue having the form of part of the sur- 

 face of a cylinder. This segment passes from the leaf base into the outermost zone 

 of the stem, uniting right and left with the strands of this zone. Then, continuing 

 in an obliquely descending direction, it passes on into the second zone and so on 

 until it reaches the longitudinal axis of the stem, where it unites with other leaf- 

 trace bundles and loses all individuality." 



Miss Shove found that the steles in the stem were both mesarch and endarch 

 in structure. The protoxylem is found in groups of two or more spiral tracheitis, 

 some of them at the periphery and some in the center of the stele. The number of 

 protoxylems varies with the size of the stele, the larger ones usually containing five 

 or six such groups. The earliest protoxylem appears at the periphery of the stele. 

 Protophloem is developed upon the outer side of the stele in the form of discontinu- 

 ous, small, thick-walled elements, which Miss Shove regards as sieve tubes. This 

 protophloem does not occur upon the inner side of the xylem. A remarkable pecu- 

 liarity of the bundle is the fact that the secondary sieve tubes are formed outside the 

 protophloem instead of within it. The phloem is of greater breadth on the outer 

 side of the stele than on the inner. No endodermis could be detected about the 

 steles in the stem. The usual absence of sclerenchyma was noted for the stem. Miss 

 Shove was unable to determine the nature of the apical meristem and the question 

 still remains open, whether the stem grows from a single apical cell or from a group, 

 such as is found in the larger roots. 



It appears from the account of both the older and more recent investigators 

 that the complicated system of concentric meshed zones in the adult stem of Angiop- 



