378 SUMMARY OF CURRENT RESEARCHES RELATING TO 



before differentiation into regions has begun. The cortex shares in 

 forming the cortex of the root. 8. Mucilage ducts originate both 

 achizogenouslj and lysigenously, generally the former. 



Marattia is characterized by a marked instability. Such an insta- 

 bility is found in the root, structure of Ophioglossacese, the protoxylem 

 position of Dicksoni8e s and in the variable apical meristem of tern game- 

 bophytes. < lombined with this instability in Marattia is the indefinitenesa 

 of the medullated monostelic stage. The Marattiacese have retained 

 many characters of the stock from which branched off the ( >phioglossaceae, 

 then the Psaronieae and Cyatheaceae. 



Mechanism by which Fern Fronds roll up.*— W. Schmidt discusses 

 the question of the means by which certain ferns roll uj> their fronds ; 

 whether it be a hygroscopic phenomenon, due to changes in the hygro- 

 scopic condition of the cell-wad. or whether it lie a cohesion phenomenon, 

 due to changes in the quantity of the cell-sap. The cohesion theory was 

 invented by Kamerling, and the name refers to the strong cohesion of 

 the primordial utricle to the cell-wall. As the cell-sap is reduced by 

 evaporation, the cell-wall is dragged in owing to atmospheric pressure 

 and does not separate from the contracted primordial utricle. The author 

 adopts the second theory, and summarizes his conclusions as follows:— 

 1. The rolling up of the desiccated fronds of Geterach qfficinarum, Poly- 

 podium vulgare, Asplenium Trichomanes and A. ruta-muraria is due to 

 cohesion and not to hygroscopic mechanism. 2. Steinbrinck's methods 

 were very successful in proving the existence of cohesion-mechanism. 



3. Very satisfactory results were obtained by a new method which per- 

 mitted the making of observations not only on sections but also on intact 

 fronds by such dehydrating agents as strong glycerin, etc. 4. The in- 

 fluence of turgor on curling fronds must not be overlooked. 5. The 

 curling movement of the fronds is in keeping with the anatomical 

 structure. 



Pteropsida.f — E. C. Jeffrey replies to criticisms which have been 

 levelled at the great group of vascular plants defined as Pteropsida. 

 and gives the following summary of his views. 1. The Pteropsida 

 represent a great natural phylum of vascular plants characterized by dorsi- 

 sporangiate sporophylls and by palingenetically large leaves, as inferred 

 from their anatomical relations. 2. The pith of the Vasculares, in all 

 cases where definite evidence is available, is an inclusion of the funda- 

 mental tissue of the cortex on the part of the stele. 3. The concentric 

 type of tubular central cylinder is more ancient than the collateral and 

 antedates the latter, as is shown by the persistence of the concentric 

 condition in many leaf -traces, where it has become obsolete in the stem 



4. So far as the primary bundle system of the Vasculares is concerned 

 they present a reduction series, in which the ferns and lower Gymno- 

 sperms (Archigymnospernife) represent the earlier and more complex 

 stages, and the higher G-ymnosperms (Metagymnospermre) and dicoty- 

 dons the phases which are more recent and more simplified. 



* Beih. Bot. Centralbl., xxvi., Abt. 1 (1910) pp. 476-508. 

 t Bot. Gaz., 1. (1910) pp. 401-14 (1 pi.). 



