FILICES. 171 



structure. I may take this opportunity of saying that I am indebted to 

 the kindness of Herr Schwacke of Rio Janeiro for some notices of stems 

 of Psaroniae preserved in the museum in that city. The chief specimen, 

 forty centimetres in length, appears from the drawing before me not to 

 belong to the same species as the disks in the British Museum. Its 

 history unfortunately is not certainly known, but various fragments of 

 Psaroniae have been discovered in the provinces of Sao Paolo and Parona, 

 in company as usual with Araucaroxylon. 



The centre of the stem thus constituted is surrounded by a rind of 

 parenchymatous tissue of varying thickness, which is always so pierced and 

 traversed by countless crowded unbranched adventitious roots running 

 almost perpendicularly downwards, that its tissue appears as if it were only 

 complemental tissue between the transverse sections of the roots. Each of 

 these roots has a central stellate usually hexarc strand of xylem inclosed 

 in a primary cortex of compact or loose parenchyma, which is surrounded 

 on the outside by a strong dark-coloured cylinder of sclerenchyma ; the 

 phloem-strands in the sinuses of the xylem are scarcely ever preserved. The 

 sclerenchymatous tissue has no very sharply defined boundary-line, but 

 appears to be in immediate communication with the tissue of the stem 

 traversed by the roots ; this, according to the analogy of Ophioglossum and 

 of the roots which grow downwards in the base of the stem of tropical 

 Lycopodiae, can only be due to very intimate secondary coherence of the 

 two parts. Stenzel 1 it is true takes a different view of the matter; he 

 speaks of the roots, so far as they are inclosed in the cortical tissue of the 

 stem, as root-primordia ; but this view is not easy to reconcile with what 

 we know from more recent researches of the mode of formation of adven- 

 titious fern-roots. The sclerenchymatous envelopes of the roots are seen 

 on the transverse section as delicate brown circles ; the pitted appearance 

 which they produce on the surface of the section has given occasion to com- 

 parison with the breast of the starling, and in Germany to the trivial name of 

 Staarstein. We should expect to find everywhere between the transverse 

 sections of the roots the transverse sections of the leaf-traces cut through at 

 different points in their course; but they are not to be seen, or only to a 

 very limited extent and only in the vicinity of the axis of the stem. It is 

 conceivable that the trace on issuing from the leaf separates at once into 

 numerous bundles of minute size on the transverse section, and that these 

 are lost to sight amid the mass of roots. On the other hand, we may 

 assume with Stenzel a considerable growth in thickness of the peripheral 

 parenchyma, the entire cortex, and that this takes place also at the 

 surface where the leaves are detached from the stem and causes the 

 extremities of the bundles gradually to disappear within it. 



1 Stenzel (1). 



