NS 
1898-99.] MORPHOLOGY OF THE CENTRAL CYLINDER IN THE ANGIOSPERMS. 607 
Possibly misled by Hofmeister’s older account, already referred to, 
Van Tieghem* has described the large axial strands as primitive, and 
the strands outside as secondary cortical steles derived from these. A 
study of development shows that, in reality, the external strands are 
primitive, as may indeed be inferred from the fact that the traces of the 
roots and leaves are directly attached to them even in the mature 
rhizome. The axial concentric strands, on the other hand, are ot later 
origin, and are to be regarded as medullary bundles. 
It will probably be obvious to the reader who has followed the 
foregoing account and examined the accompanying photographs, that 
the development of P. aguzlina offers little support to Van Tieghem’s 
hypothesis of Polystely. The writer hopes to publish in the near 
future, an account of the stelar development of a number of cryptogamic 
forms of the so-called polystelic type, in which the arrangement of 
the nascent fibro-vascular apparatus is identical with that found in 
P. aquilina. The young stelar system of the so-called polystelic type 
among the Filicales would appear to be characteristically tubular, and 
the writer” has already suggested on that account, that it may be 
appropriately designated siphonostelic. 
PRIMULACE#. 
Having discussed in a general way the development of the so-called 
polystelic type in the Cryptogams, we may now profitably turn our 
attention to the development of the same type in the Angiosperms. It 
was the study of the anatomy of the stem of a large number of species 
of the genus Primula which led Van Tieghem to propose the doctrines 
in regard to the morphology of vascular strands, which are at present 
so generally accepted by anatomists. Although derived, in the first 
place, from an examination of certain Angiosperms, Van Tieghem’s 
hypotheses have been extended by their author also to the Cryptogams. 
Van Tieghem describes two main types of cauline anatomy as 
occurring in the Linnzan genus, Primula. In one type, the central 
cylinder becomes dilated above the cotyledons and forms a medulla” 
This medullated monostelic central cylinder does not” subsequently 
undergo divisions. In a second type the central cylinder remains 
undilated and without a medulla for several internodes above the 
18. Op. Cit., p. 765. 
1g. Trans. Brit. Ass. Adv. Sci., 1897, p. 869. 
20. Sur. la Polystélie, p. 292. 
