r84 Mr. Thomas Hick on the 



four similar elements arranged in a radial line. These 

 have somewhat thickened walls, and are clearly distinguish- 

 able from the elements around them. 



In dealing with the Primary Structure of the Stem of 

 Catamites reasons were adduced* for regarding the " melas- 

 matic " tissue as a part of the cortex and not of the central 

 cylinder or stele. Hence in the leaf it must be referred to 

 the mesophyll and not to the strand of tissue which contains 

 the vascular bundle. 



(iv.) Within the " melasmatic" layer we have a circular 

 group of apparently cellular elements, in which is placed, 

 excentrically and nearer to the lower side, the transverse 

 section of a very delicate vascular bundle. The xylem part 

 of this may be recognised, but the accompanying elements 

 can scarcely be distinguished as phloem, and the orienta- 

 tion is, therefore, doubtful in this instance. In other sections, 

 however, the xylem is seen on the upper side of the strand 

 and the phloem on the lower. 



Summarising this description, it may be said that the 

 leaf-section here represented has a radial rather than a 

 dorsiventral organisation, and that it is made up of the 

 following parts : — 



(a) A central cylinder or stele, in which is a single, 



delicate, excentrically placed vascular strand of 



the collateral type. 



{b) A zone surrounding this, corresponding to the 



cortex of the stem, in which we can distinguish 



(a) An inner layer composed of "melasmatic" 



tissue, and 

 (j3) An outer, thicker layer, composed of assimi- 

 lating tissue. 

 (c) A single-layered epidermis. 

 It may be added that the section measures § of a milli- 



* Loc. cii., p. 162. 



