214 Physiologie. — Palaeontologie. 



greatest between ions of different valency, though not altogether 

 absent between ions of the same valency. They regard the expla- 

 nation of antagonism put forward by SzUcs, based on Pauli's view 

 of absorption, as the most plausible one. Pauli regards the plasma 

 raembrane as acting as a carrier of ions into the interior of the 

 cell and as forming Compounds with the ions, the latter entering 

 by virtue of the reversibility of the process. Szücs, adopting this 

 view, points out that inorganic electrolytes insoluble in lipoids can 

 in this way enter the cell, and concludes that if there is outside 

 the cell a mixture of salts containing two different ions, both car- 

 ried in by the same radicle of the plasma membrane, these ions 

 must naturally hinder one another's absorption, since each will 

 combine with a part of the plasma membrane substance which would 

 otherwise be used by the other ion if that alone were present, and 

 thus the absorption of both ions is hindered. However, Cranner 

 has suggested that the cell wall plays an active part b}?- virtue of 

 the lipoid substances which it is said to contain in addition to cel- 

 lulose and pectin; and it must be left for future work to localise 

 definitely the part which the various membranes surrounding the 

 protoplast actually play in the phenomena of antagonism. 



F. Cavers. 



Bancroft, N., A contribution to our knowledge oi Rachi- 

 opteris cylindrica, Will. (Ann. Bot. XXIX. p. 531. Oct. 1915.) 



The distribution of Rachiopteris cylindrica appears to be restric- 

 ted to the Halifax-Huddersfield area, where it occurs in the Halifax 

 Hard ßed of Lower Goal Measure Age. It is found in the nodules 

 of the coal seam, and its excellent preservation suggests that it was 

 petrified more or less in situ. 



The Sterns and their corresponding petioles are referred to two 

 types, described as « and ß respectively. « stems are characterized 

 b}^ a well-developed xylem Strand exhibiting a marked tendency 

 towards mesarch structure, with differentiation of the central Cle- 

 ments; the inner and middle cortical areas have fairly thick walled 

 cells, while the outer cortex is composed of a few layers of thin- 

 walied cells, suggestive of an assimilatory tissue. « petioles also 

 have well-developed xylem Strands, frequently with distinct diarch 

 structure; their cortex is like that of « stems. 8 stems possess only 

 a small monarch, centrarch xylem Strand. The cortex is wide and 

 composed of thin-walled cells; the middle area is more or less lacu- 

 nar, and the outer layers of the stem seem to be of the same 

 nature, as those of « stems. The corresponding petioles have also 

 a wide cortex, and a reduced xylem Strand which is always monarch. 



Associated with stems of R. cylindrica are numerous small 

 roots. diarch and typically fern-like; similar structures were also 

 observed in various stages, arising endogenousU^ from both « and 3 

 stems, the roots of both types being similar in structure. 



In fairly constant association with the stems of R. cylindrica 

 are "axes" of varying sizes, and detached sporangia similar in type 

 to those associated with Botryopteris ramosa, B. hirsuta, and B. 

 antiqua. The similarit^?- of the cortex to that of « organs suggests 

 that these axes are branches of the primarj?- « petioles. 



The occurrence of the « and B types of stems and petioles sug- 

 gests three possibilities. Firstly that the}'- represent different regions 

 of the same plant fcompare Psilotuni and Hottonia)\ but no transition 



