PROGEESS OF MICROSCOPICAL SCIENCE. 95 



" 4tli. That pus diifers from white blood corpuscles. 



" a. — In the disturbance which it sets up when introduced in these 

 vessels. 



" h. — In the loss of the power of organizing. 



" c. — In the frequent acquisition of contagious properties. 



" These are some, though by no means all, the reasons why I 

 consider that pus is not the same thing as a white blood corpuscle. 

 If I have established the point, it will be something gained; if I 

 have failed, I would esteem it a favour to be shown my error." 



Structure of Boehneria nivea. — The structure of the aerial stem of 

 Boehvieria nivea, a plant belonging to the nettle family, yielding the 

 well-known China grass or Ithea fibre, was described by Mr. H. 

 Pocklington, at a late meeting of the Leeds Naturalists' Field Club, 

 as follows : — The central pith is peculiarly white and glistening to 

 the naked eye. This is doubtless due to the excessive tenuity of the 

 walls of the cells composing the medulla, to their being devoid of all 

 proteinaceous contents, and to their inclusion of nothing but air when 

 in the dry state. Most of the light incident upon them when viewed 

 in situ will be totally reflected from the surfaces of the air within the 

 cells, and thus give them the appearance of being illuminated by a 

 clear lunar light from within. The medullary sheath is well 

 developed, and consists, excluding the ordinary woody fibre, of large 

 trij)le-si)iral vessels, boldly barred bothrenchyma and long cylindrical 

 cells containing a yellowish fluid soluble in alcohol. The fil3re of the 

 spiral vessels is strong, and easily separates from the primal wall of 

 the cell, and the " barred " vessels are somewhat remarkable for their 

 coarseness when contrasted with the vessels of the woody zone. The 

 yellowish oil has not been investigated as yet, but appears to be a 

 chlorophylloid product. The woody zone is well developed, and is 

 remarkable for the nature of the cells of which it is composed. The 

 normal spindle-shaped inactive much-thickened wood fibres are here 

 replaced by thin-walled prosenchymatous cells containing, beside pro- 

 teinaceous matter, large quantities of starch granules, and by less 

 obviously wood-cells, minutely porous and also containing starch. 

 Starch-bearing wood-cells have been described by Hassall* and myself f 

 as occurring in certain roots and rhizomes, but they have not, so far as I 

 know, been hitherto described as occurring in aerial stems. The occur- 

 rence of them in roots is entirely unnoticed in our text-books, and is 

 unknown to many botanists of extensive knowledge. The medullary 

 rays are not evident in transverse section, but may be easily recognized 

 in longitudinal sections. They are very much longer than broad, 

 sometimes thickened, and contain little beside sap and starch. The 

 bothrenchyma is interesting. The pits are oval, sometimes complete 

 pores, and in the centre of a discoid, rhomboidal, or polygonal ternary 

 deposit, with an irregular spiral of secondary dej)osit running between 

 them. These are in fact very good examples of what are known as 

 bordered pits, but must not be confused with the glandular pleuren- 

 chyma of conifers. The starch granules are varied in shape. The 



* ' Adulteration Detected.' t ' rharniaoeutical Journal,' 187*2-3. 



