Table 3. Observed Frequency of Length of Tunnels in the Silica Layer in Rice Husk Samples^a.

	length of tunnel/nm
	<2	2–3	3–4	4–5	5–6	6–7	7–8	8–9	9>	mean length/nm	standard deviation/nm
network 1	0	37	63	54	51	31	11	2	0	4.5	1.4
network 2	0	31	61	59	53	17	5	2	0	4.4	1.2
network 3	0	15	67	68	49	24	5	4	0	4.6	1.3
network 4	0	19	36	40	47	21	2	8	3	4.9	1.6
total	0	102	227	221	200	93	23	16	3	4.6	1.4

^aNetworks 1, 2, 3, and 4 correspond to the graphs in Figures 1e,f, S5k,l, respectively.