406 BOTANICAL GAZETTE [DECEMBER 
presented, as in Primula and Pteris, each segment being in 
every respect a stele. If these steles fuse laterally, thus forming 
a ring with internal and external phloem, the gamostele is pro- 
duced as illustrated by Marsilia. Again, when parenchyma seg- 
regates in the axis of the monostele, and the vascular ring is 
broken into strands by ectad extensions of this pith (the medul- 
lary rays), we have the medullated monostelic type, such as is 
common in phanerogams. It is to be noted that the medullary 
and cortical tissues are considered by both these botanists to be 
of morphologically different value. Now by the bending in of 
the endodermis of the medullated monostele between the 
bundles, and the fusion of thé ends of adjacent groups on the 
centrad side of the bundle, so that each bundle has its endoder- 
mal sheath, and medulla and cortex become continuous, the 
schizostelic or astelic type results. Of this phenomenon Ranun- 
culus and Equisetum afford examples. A modification of this 
type, the gamodesmic-schizostelic, is produced by the lateral 
fusion of these endodermal sheaths, so that there is a common 
internal and a common external endodermis. If the internal 
endodermis degenerates, as it does in Z. arvense, then there is 
evidently a simulation of the medullated monostele. It is fair 
to add that Strasburger dissents 3* from the last two types des- 
cribed, the astelic and the gamodesmic, for he regards the endo- 
dermal sheaths about the bundles in the first of these, and the 
internal endodermis in the second, as not morphologically 
phloeotermal, but originating from specialized stelar cells. 
The researches of Gwynne-Vaughan* and Jeffrey # have 
shown that the phenomena said to lead up to polystely do not 
occur in Primula and Pteris. If the polystelic conception falls, 
obviously gamostely goes too. Further, astely has been shown, 
where it occurs in Equisetum and Ranunculus, to be preceded by 
the gamodesmic appearance. Later the internal and external 
3* STRASBURGER : of. cit. Pp. 442. 
; = OWE Vepenae < Polystely and the genus Primula. Ann. Bot. 11: 307- 
% JERFREY : Morphology of the central cylinder of angiosperms. Trans. Canad. 
Inst. 6 :—. (1-40) 1900. 
