154 NATURAL SCIENCE [March 



mncli, and views of the relation between turgor and growth have 

 materially changed within the last ten years. The experiments now 

 before us were undertaken to ascertain the iniluence of various 

 chemical elements on the turgor of the plant-cell. The results were 

 however almost entirely negative. Potassium alone showed any 

 direct influence, its removal as a food-substance being followed by a 

 diminution of turgidity. 



Potassium presented in solution to the roots of plants causes the 

 cells of both root and stem to show a higher turgor than they do 

 when it is replaced by sodium. From the analysis of the sap, the 

 writer concludes that the influence is a direct one. When offered 

 to the root, the potassium salt is taken up and stored in the cell-sap, 

 where it becomes an important part of the osmotically active material 

 which keeps the cell and plant turgid. It is difficult to understand 

 tliis decided insistence of the plant for potassium, and the uselessness 

 of the far more plentiful and physically lighter sodium. 



The PtiDDLE OF Oryptodiscus 



In 1864 Professor James Hall figured a peculiar fossil from the 

 Niagara Limestone, apparently of Wisconsin, and gave it the name 

 Cryptodiscus (Fig. IV). No notice was taken of this, and it was not so 

 much as mentioned by Mr S. A. Miller in the various editions of his 

 catalogue of North American fossils. Mr Miller himself, however, in 

 1892 figured a portion of a similar fossil from the Niagara Lime- 

 stone of Indiana, indicating it as "??????? ." In the Journal 

 of Geology (Vol. V., No. vii., pp. 744-751), published at the close of 

 1897, Mr Stuart Weller, of the University of Chicago, describes and 

 figures four difi'erent forms of the so-called Cryptodiscus, from the 

 dolomitic Niagara Limestone of -Toliet, 111., and applies to them as 

 many specific names. No diagnosis of Cryptodiscus is given, so that 

 it is a little out of place for Mr Weller to say that Hall's name was 

 "never properly published." The fossil may, however, be described 

 as composed of four plates, each roughly forming the quadrant of a 

 circle, opposed by their straight edges, meeting around the centre in 

 a downward prolongation of square or sub-circular section, in which 

 a central canal is left, and often forked or extended in several 

 branches on their outer margins. Hall regarded Cryptodiscus as 

 " the calyx of a Crinoidean ? of a new and peculiar type " ; but Mr 

 Weller's interesting article is largely devoted, as its title indicates, 

 to proving that the fossils represent " the casts of the gastric cavities 

 of medusae." We are spared the trouble of criticising this not very 

 plausible suggestion, through a footnote added by Mr Weller on 

 sending the paper to press. Specimens in the collection of Mr E. E. 

 Teller, of Milwaukee, " seem to establish the fact that Cryptodiscus 



