TRANSACTIONS OF SECTION K. 939 



In the peduncle of the male cone of Stangeria the single cylinder consists in 

 its lower portion of bundles which, by their irregularly curved, sub-concentric, or 

 sometimes perfectly concentric contour, betray their derivation from a cylinder of 

 concentric strands like that of Medullosa Sohnsii. 



The primitive vascular bundle of the foliar organs from which that in all the 

 various foliar organs of modern Cycads has been derived is, on the view here set 

 forth, held to be the type exhibited by the leaf of Lyginodendron (Eachiopteris) : 

 it consists of a central mass of primary tracheides with several protoxylem-groups 

 at the periphery, the whole being surrounded by phloem. 



In Xhe foliage-leaves of modern Cycads the concentric bundle becomes broken 

 up into great numbers of collateral bundles, each with a conspicuous mass of 

 centripetal primary tracheides. This very same character obtains in the foliage- 

 leaves of all species of Medullosa. 



In the cotyledons, sporojjhylls, and sporangial integuments of recent Cycads 

 many of the bundles exhibit the primitive concentric type of structure, with the 

 modification that in the cotyledon of Stangeria, the reduction in size of the 

 bundle, in the sporophyll, as in Encephalortos, the development of the secondary 

 centrifugal xylem has caused the disappearance of the central primary xylem ; a 

 modification which has also supervened in the case of the vascular strands of the 

 stem. Hence the vascular structure of iha foliage-leaves of the Medullosea is more 

 advanced and modified than is that of the cotyledons and sporophylls of recent 

 Cycads, and a fortiori than that of the foliage-leaf of Lyginodendron. 



The central cylinder of the stem of Lyginodendron Oldhamium has the same 

 origin as that of modern Cycads, as is shown (1) by the curved contour of the 

 various strands composing it, betraying the origin of each l^-om a concentric strand; 

 and (2) by the occurrence of inversely-orientated vascular tissue on the inner side 

 of the cylinder, abnormally in L. Oldhamium and normally in L. rohustum. 



The single stele of Heterancjium is, homologous with each single concentric stele 

 once, on this view, composing the cylinder oi Lyginodendron, a,s with each such 

 stele in Medullosa Solmsii and M. avglica. 



Three stages of advancement are, therefore, to be noted in the vascular struc- 

 ture of this great phylum :— 



The Filices possess a vascular system in essentials wholly concentric ; in the 

 Cycado-jilices the collateral character first makes its appearance ; in Cycads the 

 collateral strongly predominates, while the concentric has almost died out. 



5. On tlie Structure of the Stem of Angiopteris evecta, Hoffm. 

 By R. F. Shove, Girton College, Cambridge. 



This paper deals with the anatomy of the stem and roots of a plant of 

 Angiopteris evecta from Ceylon. The older part of the obliquely ascending axis 

 exhibits a distinct dorsiventrality and gives off numerous roots from the lower 

 surface ; in the younger part of the stem the structure becomes more radial and 

 the roots are much less abundant. 



The mode of origin of the leaf-traces and their connection with the stelar frame- 

 work in the stem, which has the form of a series of inverted funnel-shaped zones, is 

 worked out in detail, the result in a few points differing somewhat from those 

 obtained by Mettenius. 



The steles of the stem are both mesarch and endarch in structure, but the 

 protoxylem groups occupy for the most part a peripheral position. The earliest 

 protoxylem appears along the inner edge of the steles, while the protnphloem arises 

 on the outer edge of each stele as a discontinuous arc of small and rather thick- 

 walled elements. This arc of protophloem is never completed round the stele, but 

 the next stage in the development of the tissues after the appearance of the pro- 

 toxylem is the differentiation of large sieve-tubes external to the protophloem. 



Air-roots and earth-roots were anatomically investigated, and the origin of the 

 latter was traced from the vascular lattice-work of the stem. Several initial cells 

 were recognised in the apical region of the stem. 



