Proceedings. ii 



to rotate about a vertical axis through its centre. But, as 

 an illustration of the theory of secular stability, this is not 

 so good as the bowl, since the frictional forces will now 

 depend on the absolute and not on the relative motion of 

 the particle. 



Mr. Charles Bailey, F.L.S., made some remarks on the 

 anatomy of the Iris sibirica, Linn., a plant which occurs in 

 the northern hemisphere, from Alsace eastwards to Siberia, 

 northwards to Scandinavia and the Baltic provinces, and 

 southwards to Italy and Servia. The young roots are 

 noticeable for their clearly-defined endoderm, made up of a 

 single layer of thick-walled cells. The creeping rhizome is 

 remarkable for its large rhombic crystals, which are con- 

 tained within cells of corresponding size ; these crystals are 

 the equivalents of the smaller and much shorter crystals in 

 the epiderm of the bulb of the onion, and of the raphides of 

 many other plants. These long crystals are not confined 

 to the rhizome, as they are met with in the leaf, stem, and 

 ovary, one of the latter being figured in Dr. Dodel's series of 

 seven large chromo-lithographs, exhibited at the meeting. 

 In this Iris, as in other flat-leaved monocotyledons, the 

 leaves are divided by several parallel longitudinal bundles, 

 which form the ridges so plainly to be seen and felt in the 

 leaves of the dried plant ; it is these parallel ribs which 

 give the mechanical assistance which enables the long narrow 

 leaves to maintain their erect position when growing. 

 Large air-spaces, bounded by distorted or collapsed cells, 

 occur between the ribs. In most leaves the differentiation 

 of the vessels progresses, ordinarily, from the median rib 

 towards the lateral ribs successively ; but in Iris sibirica 

 the vessels of the median rib appear the last, as shown by 

 a section through the rhizome at a point where a leaf-bud 

 was being given off, the arrangement of the leaves in the bud 

 being equitant. The epiderm of the leaf presents an un- 

 usual arrangement of its flat elongate cells, and of the air- 



