which factor is nested ?

From: fred (fred_at_patatipatata.fr)
Date: 01/10/05 

Date: Mon, 10 Jan 2005 17:33:55 +0100

Dear all,

I have difficulties to manage an anova with the following dataset which
concern some plants individuals obtained by known crossing of parents :

2 factors are first considered :
the site of growth : X, Y or Z
the crossing : 9x34 9x35 9x36 7x25 7x26 7x27
in this coding, first number is the father and last number is the mother
of the considered individual

A last factor is considered at the end of the experiment :
the resistance to a virus : R or S
The point is that only crossings with male 9 are resistant (R) and only
crossings with male 7 are sensible (S)

A biological immunological variable (bio) was measured on those plants
in following way :

3 individuals of each crossing were measured in each locality so the
table looks like

Individual Crossing Site Resist
1 9x34 X R
2 9x34 X R
3 9x34 X R
4 9x35 X R
...
54 7x27 Z S

How to analyse the variability of the 'bio' variable taking into account
all the information I have. It *seems* to me that the 'Crossing' factor
is nested in the 'Resist' factor or can also be nested in 'Site' : am I
right ?

Is the following model right, or am I lost in nested anova's ?

bio = Crossing %in% Resist + Crossing %in% Site + Resist + Site

Do you think I should separate informations about Crossing in two
variables (Male / Female) to build a more clever model ?

Many thanks in avance for your help and clever lights
(My software is R)

Fred