246 MR. C. DARWIN ON THE ACTION OF CARBONATE 
were coloured blue. The tips of the roots of Pastinaca sativa 
turned dark brown by a similar immersion ; but this was due to 
the formation of orange-brown balls of matter near the vaseular 
bundle; higher up the roots there were no granules in the exte- 
rior cells. The tips of the roots of Lamium purpureum, after an 
immersion of 18 hours in a solution of 4 to 1000, were rendered 
brown, and the cells eontained innumerable pale-coloured hyaline 
globules. The older roots of Leontodon Taraxacum and of a Son- 
chus had their tips turned brown by the solution. With Lactuca 
sativa the tips were rendered opaque; but much granular matter 
was not deposited except in that of one rather thick leading root, 
and here short longitudinal rows of cells containing dark-brown 
granular matter alternated with rows of colourless cells; the 
almost loose cells of the root-cap likewise contained brown gra- 
nules. In the several following cases a much more strongly 
marked effect was produced by the solution. 
Urtica.—This plant, the common nettle, shall be first consi- 
dered, as it is distantly allied to the Euphorbiaces, though the 
roots are not so much affected as in succeeding cases. Several 
roots were left for 27 hours in a solution of the carbonate (4 to 
1000). In one of them the exterior cells were plainly tinted of 
a brown colour in many longitudinal rows, but they contained 
' no visible granules; and these rows regularly alternated with 
others formed of colourless cells. In another part of this same 
root allthe exterior cells were coloured dark brown, and con- 
tained visible granules, which were generally collected into heaps 
at one end of the cell, or were fused together in some instances 
into small brown spheres. In a second, rather thick root, there 
was à space in which all the exterior cells had become brown; 
but at no great distance rows of brown and colourless cells regu- 
larly alternated. In a third, rather thick, and in a fourth, thin 
root the alternation was extremely regular. Near the tip of a 
fifth (thin) rootlet two rows of a brown colour ran alongside one 
another in many places ; but when these and other single rows 
were traced up the root, they changed into 'colourless rows, and 
afterwards reassumed their former character. Whenever the 
root-hairs were traced down to their bases, they were seen to 
arise from colourless cell. Neither granules nor brown fluid 
were observed in the parenehyma-eells nor in those surrounding 
the vascular bundle. 
Some roots which had been left in water for several days were 
