‘ aie 
Ly 
1898-99.] MORPHOLOGY OF THE CENTRAL CYLINDER IN THE ANGIOSPERMS. 605 
Polystely in the Angiosperms. This species is chosen because the 
investigation of Leclerc du Sablon, and of the writer, show it to be quite 
typical of the polystelic Pteridophyta. The form selected presents, 
meoreover, the phenomenon of Polystely in a high state of complexity, 
_and its cosmopolitan occurrence will make it easy for other botanists to 
verify, if so minded, the accuracy of the description given here. 
Leclerc du Sablon™ has correctly described the transitional region of 
the young stem of P. aguzlzma. Higher up, and immediately above 
where the first leaf-trace is given off from the concentric central cylinder, 
the phloém sends a process into the centre of the vascular axis of the 
strand. When the gap, caused in the axis by the exit of the foliar 
tracheids, is closed again, the central phloém remains included, forming 
a sort of pith. The exit of the traces of several subsequent leaves 
causes similar gaps in the continuity of what is now the vascular tube, 
and through these gaps the internal phloém cormmunicates with that 
outside. Photograph 1, plate 7, shows the structure of the young 
stele, at a point where the second leaf-trace has just passed off. The 
central island of small-celled bast can be distinguished, surrounded by a 
ring of tracheids, which is interrupted opposite the leaf-trace, 4 At the 
level of the fourth or fifth leaf, the fundamental tissue penetrates to the 
centre of the stele through the foliar gaps, forming, henceforth, a 
continuous core within the internal bast. At this stage the stelar system 
is a hollow cylinder, perforated by gaps above the points of origin of the 
leat-traces. Leclere du Sablon’ correctly describes it as being, in this 
phase, like the stelar tube, which is permanently present in the stem of 
Marsilea. The writer has not been able to distinguish any evidence of 
the repeated bifurcation of the young central cylinder, described by Van 
Tieghem as characteristic of his polystelic type. On the contrary, both 
the writer's observations and those of Leclerc du Sablon seem to show 
that the young stelar system of P. aguzlina is of the type described by 
Van Tieghem as gamostelic. That term, however, can hardly be 
correctly used to describe the structure of the central cylinder of this 
species, because it implies the fusion of steles, originally separate, of 
which there is no indication whatever in this form. The writer", has 
previously suggested the term siphonostelic as more accurately 
describing the conformation of the young stelar system in the so-called 
polystelic Filicales; for his studies on the development of a number of 
12. Op. Cit., p. 3. 
Tar Ops Cit. 5p; 5: 
14. Trans. Brit. Ass. Adv. Sci., 1897, p. 869. 
15. Mem. Bos. Soc. Nat. Hist. V.5, No.5, p. 160. 
