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1898-99.] MORPHOLOGY OF THE CENTRAL CYLINDER IN THE ANGIOSPERMS. 627 
The writer has already referred to the inadequacy of Van Tieghem’s 
conception of the so-called polystelic type. It seems inappropriate to 
designate the young tubular central cylinder of Pferts aguzltna and 
Primula auricula as gamostelic, since the use of this term implies Van 
Tieghem’s conception of the repeated bifurcation of the primary stele 
and the subsequent union of the fractions to form a stelar tube. The 
study of development shows the tubular condition to be in reality primi- 
tive and the writer® has, previously, in view of that fact, suggested that 
this form of central cylinder be designated siphonostelic. 
The studies of Gwynne- Vaughan and of the writer on the Primulacee, 
Halorhagidacez, and Saxifragaceze seem to show that the siphonostelic 
type of central cylinder, with internal phloém, is not to be regarded as 
primitive in the case of the Angiosperms, but that it is derived from a 
siphonostelic type in which there is primitively no internal phloém. This 
conclusion is justified by the fact that the young stelar tube is some- 
times actually without internal phloém, eg., Przmula japonica, P. 
fartnosa, and Gunnera scabra, and by the fact that, even when the young 
stelar axis is concentric from the first, the leaf-traces retain the 
apparently ancestral collateral type, ¢.g., Primula Auricula. Gwynne- 
Vaughan attributes the appearance of internal phloém in the central 
cylinder of certain Dicotyledons to an effort to make up for the loss 
of a cambium, a feature correlated with so-called polystely. 
I[.—The writer’s study of the development of the so-called astelic 
central cylinder of certain Ranunculacee and Nymphezaceze shows that 
in this type, the course of events is practically the same as that in the 
so-called polystelic axis, vzz., that the epicotyledonary stele becomes in 
the young plant a tube interrupted by foliar gaps. The tubular 
character of the stelar system may be subsequently disguised by the 
increasing complexity of the arrangement of the fibro-vascular strands, 
but in all such cases the collateral stelar tube may be recognized in the 
young axis. The writer has not been able to find any evidence in the 
facts of stelar development in seedlings, supporting Van Tieghem’s 
statement that his astelic type originates by the separation of the 
phlceoterma into segments, which unite around the individual bundles. 
Neither do his observations accord with the more recent description 
given by Van Tieghem” of the astelic type, in which he states that 
astely or schizostely as he now prefers to call it (adopting a suggestion 
of Strasburger’s), originates by the stele breaking up into as many 
meristeles as it contains bundles. The young stele in these cases is 
49. Trans. Brit. Ass, Adv. Sci., 1897, p. 869. 
50. Eléments de Botanique, p. 179. 
