252 Pteridophyten. 



collection of fossil slides two, one of Stigmaria and one of Spheno- 

 phylliim , were found both showing the midlle lamella as a closing 

 membrane. The author, however, maintains that Haltt fails to see 

 that a certain amount of disintegration of the primary wall actually 

 takes place, for the primary laj^ers are thicker where the bars join 

 than where they are separate. 



Isabel Browne (University College London). 



Bower, F. C, On Medullation in the Pteridophy ta. (Ann. 

 Bot. XXV. p. 555—574. pl. XCVII. 1911.) 



The author opposes Jeffrey's view that the pith is in all cases 

 where definitive evidence is available, an inclusion of the cortical 

 tissues in the stele. It is held that a pith may be extrastelar, as in 

 the rhizomatous solenostelic Ferns, or intrastelar as in the Lepido- 

 dendraceae or the pith of one and the same specimen may be partly 

 extrastelar and partly intrastelar in origin as appears to be the case 

 in certain Ophioglossaceae. It is thought likely that an upright micro- 

 phyllous stock favours intrastelar medullation and a creeping mega- 

 phyllous stock extrastelar medullation. In upright megaphyllous Stocks 

 and in creeping microphyllous ones the pith may be partly extra- 

 stelar and partly intrastelar, the relative development of the two 

 kinds of pith depending on the balance between these two factors 

 at the phylogenetic time at which medullation was initiated; for, 

 when once a type of medullation has been initiated it seems to be 

 retained even when the position of the stock is subsequently modified. 

 It was found that no extrastelar pockets were found in connection 

 with the first minute scale leaves of Botvychium Limaria ; at this 

 level there is a small intrastelar pith completely cut off from the 

 cortex; in connection with the larger leaves extrastelar pockets 

 encroaching on the stele are formed, though owing to the imper- 

 fectness of the endodermis the limits between extrastelar and intra- 

 stelar pith are not recognizable they were probably at first delimited 

 by an endodermal sheath. The question as to whether the endoder- 

 mis is an immutable barrier between stelar and extrastelar tissue is 

 left open. 



The establishment of the phyletic history of the pith in any one 

 line of descent has little bearing, save indirectly as an analog)' on 

 the history of the pith in another unless it be proved that the pith 

 originated before the Separation of the Stocks in question. As regards 

 the Filicales , Equisetales , Sphenophyllales , and Lycopodiales there is 

 no evidence in favour of their descent from a common medullated 

 ancestor. The Status of the pith in the higher Flowering Plants is 

 to be decided in accordance with the manner in which medullation 

 was initiated in the ancestral primitive Seed Plants such as the 

 Pteridosperms; it does not depend on the relationships obtaining in 

 solenostelic Ferns, unless it can be shown that such forms and the 

 higher Seed Plants had a common medullated ancestor. 



Finally attention is once more drawn to Gwynne Vaughan's 

 extreme examples of involution of the superficial tissues of the stem 

 into the pith in certain Ferns. 



Isabel Browne (University College London). 



Christensen, C, Pteridophyta in insula Quelpaert a cl. 



