XXX] SUTCLIFFIA 155 



In the arrangement of the bundles and in the structure 

 of the ground-tissue the petioles of Rachiopteris Williamsoni 

 agree with those of Myeloxylon. An outstanding feature of 

 the vascular strands of the former is the occurrence at fairly 

 regular intervals in the peripheral part of the phloem of compara- 

 tively large tubes described by me as secretory canals on the 

 ground that evidence was furnished of their development by the 

 schizogenous separation of cells to form a central canal. The 

 canals were compared with the large sieve-tubes of the Marattia- 

 ceae, but with the qualification that ' their mature form and their 

 manner of development are strongly suggestive of small secretory 

 canals.' Nothing was known as to the stem which bore these 

 petioles until Scott's discovery of Sutcliffia with vascular bundles 

 in the cortex and leaf-bases of the same type as those of Rachio- 

 pteris Williamsoni. As Scott says, there are a few distinguishing 

 features which suggest that R. Williamsoni is not specifically 

 identical with the petioles of Sutcliffia insignis, though the agree- 

 ment is such as to justify the substitution of Sutcliffia for Rachio- 

 pteris. The tubular elements in the phloem which I considered 

 to be secretory canals are regarded by Scott and Miss de Fraine 

 as sieve-tubes. 



Miss de Fraine gives an excellent summary of our knowledge 

 of the genus and discusses,, in the light of the additional facts 

 furnished by the second stem, the position of Sutcliffia in a phylo- 

 genetic series. The new form strengthens the comparison insti- 

 tuted by Scott between Sutcliffia and Medullosa and gives support 

 to a close connexion between the Medulloseae and the Cycadaceae. 

 Scott lays stress on the fact that the Medulloseae, except Sutcliffia, 

 are polystelic, while the Cycads, at least the adult stems, are 

 monostelic. The views of Worsdell and other botanists who 

 believe that the Medulloseae and the Cycads are intimately related 

 are discussed on another page: in reference to these views Miss 

 de Fraine adds a caveat as to the danger of attaching excessive 

 importance to evidence based on seedling anatomy when we are 

 concerned with broad phylogenetic questions. The stele of a 

 cycadean stem may be derived from a protostelic type such as 

 that of Sutcliffia by the gradual disappearance of the internal 

 tracheids : in Sutcliffia, as in some Cycads and species of Medullosa, 



