STRUCTURE.] CONIFEKOUS GLANDS SCHLEIDEN, ETC. 65 



siderably above the wall of the tube. In a specimen of Pinus 

 Strobus I have found them surrounded with an irregular 

 elevated rim, as at Plate II. fig. 7, and 8., as if the lining of the 

 tube was growing over them. It is not at all uncommon to 

 find them in what may be supposed a nascent state, merely 

 looking like tumours, with a pit in the middle, as is shown 

 at Plate II. fig. 5. 



Schleiden, while he upon the whole admits Monies expla- 

 nation, nevertheless endeavours to refer this case to his idea 

 of a universally spiral direction of secondary deposits. He 

 believes that he has seen, in Pinus sylvestris, the cells of the 

 cambium, even in the youngest annual rings, constantly 

 divided by delicate black lines into narrow spiral bauds 

 previous to the formation of pores, (as matter of course with 

 perfect homogeneity of the primary cellular membrane,) and 

 that these, which he regards as the boundaries of adjacent 

 convolutions, first disappear on the formation of pores, or 

 pits, probably glued to one another in the same manner 

 as the cells themselves, whose bounding lines frequently 

 likewise become invisible at a more advanced age ; for when 

 he isolated the cells by boiling in caustic potash, even those 

 from the outside layers of the oldest heart wood constantly 

 exhibited more or less distinctly these delicate stripes, and 

 the pores again appeared merely as narrow clefts between two 

 separating spiral coils. 



If the discs of coniferous wood are examined with a good 

 eighth of an inch object glass, and a low ocular, they will be 

 distinctly seen marked with concentric circles as represented 

 at Plate II. fig. 6. The highest oculars with a lower objective 

 will not separate the circular lines. M. Valentin, who first 

 noticed the lines (Repertorium, vol. i. t. i.), considers them to 

 be the projecting edges of numerous layers of woody matter 

 concentrically deposited round a space which they gradually 

 close up, except a narrow opening into an air chamber, the 

 layer next the centre being the youngest. I have not suc- 

 ceeded in obtaining any section which will show this structure. 



It has been imagined that this glandular Pleurenchym is 

 confined to Gymnosperms, but Dr. Brown long since remarked 

 it in Tasmannia, and Mr. Griffith found it common in aromatic 



VOL. i. F 



