[R] how to interpolate a plot with a logistic curve

[Simone Gabbriellini]

hello,

I have this simple question. This is my dataset

	size
1	57
2	97
3	105
4	123
5	136
6	153
7	173
8	180
9	193
10	202
11	213
12	219
13	224
14	224
15	248
16	367
17	496
18	568
19	618
20	670
21	719
22	774
23	810
24	814
25	823

I plot it with:

plot(generalstats[,1], type="b", xlab="Mesi", ylab="Numero di  
vertici", main="");

and try to interpolate with a linear regression with

abline(lm(generalstats[, 
1 
]~ 
c(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25)),  
lty=3, col="red");

how to interpolate the data with a logistic curve? I cannot find the -  
I suppose easy - solution..

thank you,
Simone