_Anatomical features._ Allusion has already been made to some of the more striking anatomical features; the large pith, the occasional occurrence of medullary vascular bundles, the presence of one or more cambiums, the large size of the medullary rays, etc. It is worthy of remark that the occurrence of an anastomosing system of medullary bundles is not a constant feature within a genus; in _Macrozamia Fraseri_ such a system is present, but absent in _M. Denisoni_[74]. In the pith of stems with no medullary bundles cylinders of collateral bundles may occur in connexion with a fertile shoot. These bundles arise from the inner face of the main cylinder and pass upwards as a domical system into the base of the terminal strobilus which is eventually pushed to one side by the growth of a lateral bud[75]. The secondary xylem tracheids are usually provided with several rows of bordered pits on the radial walls and resemble those of the Araucarieae[76], but in Cycads the pits are often not contiguous and less compact in their distribution. The wood of _Stangeria_ is peculiar in consisting of scalariform tracheids[77] (fig. 397). Chamberlain describes growth-rings in the wood of _Dioon_; but this is exceptional. In tangential sections of the stele leaf-trace bundles are constantly seen passing horizontally through the broad and deep medullary rays. The pith-cast of a cycadean stem reproduced in fig. 398 shows the wide meshes in the reticulum of tracheal tissue originally occupied by parenchyma, which on decay left lenticular depressions represented on the cast by tapered convex areas occasionally bearing the impress of an outgoing trace in the form of a narrow groove. The secondary phloem often rivals the xylem in breadth and is not always easily distinguishable from it; it consists of sieve-tubes, parenchyma, and fibres. The secondary cambial cylinders characteristic of _Cycas_, _Encephalartos_, _Macrozamia_, and _Bowenia_, to which reference was made in the summary of anatomical features, arise in the pericycle, and a few layers of pericyclic parenchyma occur between adjacent extrafascicular cylinders of xylem and phloem. In a stem of _Cycas media_ 35 cm. in diameter examined by Worsdell there were 12 concentric cylinders. Matte[78] and Miss Dorety[79] have described partially flattened arcs of extrafascicular xylem and phloem in the hypocotyl of _Ceratozamia mexicana_. Worsdell[80] first drew attention to the occasional occurrence of short tracheids on the inner edge of the secondary wood and to the spasmodic development of cambial arcs in the tissue between the extrafascicular cylinders forming strands of inversely orientated xylem and phloem. More recent work by Matte gives support to Worsdell’s comparison between Medullosan stems and those of recent Cycads with inversely orientated arcs or concentric vascular cylinders. The French author draws attention to the close resemblance between the seedling stems of such species as _Encephalartos Barteri_