478 SCIENCE PROGRESS. 



Cycads appears to be a case of the persistence of perixyly. 

 Remarkable transitions between Cycadean and Filicinean 

 anatomy are found in some carboniferous fossils, such as 

 Lyginodendron. 



A recent paper by Poirault on the " Anatomy of Vascular 

 Cryptogams" (24) contains several points of interest, many 

 of which however have been anticipated in his preliminary 

 notes. Poirault gives for the first time a full account of the 

 anatomy of the stem in Gleicheniacea;, which are monostelic 

 Ferns with a somewhat complex central cylinder, the pro- 

 toxylem -groups lying at or near the periphery of the wood. 

 His description suggests a considerable analogy with certain 

 fossil forms. 



Poirault has discovered in the leaves of certain Ferns, 

 such as Acrostichum, a tissue which appears to correspond 

 to the tracheal transfusion-tissue, which supplements the 

 xylem of the vascular bundles in the leaves of Conifers 

 and Cycads. 



This author has investigated the changes undergone 

 by the steles of ferns in their passage into the leaves. As 

 Haberlandt previously found, they ultimately assume a 

 collateral structure owing to the disappearance of the upper 

 part of the phloem. Poirault finds that this change may 

 take place in the petiole, or at the base of the lamina, or 

 only in the fine branches of the bundles within the 

 latter. 



Another important contribution to our knowledge of 

 the structure of vascular Cryptogams is Harvey Gibson's 

 paper on the Comparative Anatomy of Selaginella (25), 

 which for the first time enables us to form an adequate idea 

 of the range of anatomical variation within that remarkable 

 genus. It is impossible to summarise his work in this 

 article, but attention may be called to his interesting ob- 

 servation that in the basal portion of the stem of Selagin- 

 ella spinosa, the protoxylem of the stele is central not 

 peripheral, showing that perixyly is not absolutely constant 

 in the oenus. 



A short paper by Petersen (26) is of interest as showing 

 that a regular gradation can be traced from Monocotyle- 



