Q - scatterplot, plot function & trellis linear regressions???

Hi R-listers, 

Q1) What is the difference between the scatterplot and plot function? 

Q2) I am able to make a graph with the scatterplot function: 

scatterplot(DevelopIndex ~ Veg,
+             data = Turtle,
+             xlab = "Vegetation border (m)",
+             ylab = "Embryonic development index")

And have been successful. But I do not know if the lines are for: linear,
non-linear, mean, upper and lower limits or percentile? This shows side
boxplots and 4 lines. 

Yet this plot only has one regression line and no side boxplots?: 

EDIHTL <- lm(DevelopIndex~ HTL, data=Turtle)

plot(DevelopIndex~HTL, data=Turtle, pch=16, 

xlab="High tide line (m)", ylab="Embryonic development index")

abline(EDIHTL)

Q-3
I am trying to make a trellis of linear regressions. I want 3 windows
displaying 3 events of linear regression (two-way interactions). I have been
trying this:

require(lattice)

library(lattice)
trellis.par.set(col.whitebg())
scatterplot(DevelopIndex~Veg|Aeventexhumed,

+             xlab = "Vegetation border",
+             ylab = "Embryonic development index")
Error in eval(expr, envir, enclos) : object 'DevelopIndex' not found

 Please advise, many thanks.
Jean

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