no plots into viewport

Dear R Users,

could anyone help me and explain why no plot with 'plot'function is plotted 
in the viewport, but as a single plot on the next page?

grid.text() works, but neither xyplot() nor plot() do.

library(graphics)
library(grid)
library(lattice)

top.vp <- viewport(layout = grid.layout(1,2))
vp.plot1 <- viewport(layout.pos.col=1,layout.pos.row=1, name="vp.plot1")
vp.plot2 <- viewport(layout.pos.col=2,layout.pos.row=1, name="vp.plot2")
splot <- vpTree(top.vp, vpList(vp.plot1, vp.plot2))

pushViewport(splot)
seekViewport("vp.plot1")
grid.text("plot1 should be here")
plot <- xyplot(1:10~1:10)
print(plot)

Thank you very much for advice.

Michal

Michal Gallay

Postgraduate Research Student
School of Geography, Archaeology and Palaeoecology
Queen's University
Belfast BT7 1NN
Northern Ireland

Tel: +44(0)2890 273929
Fax: +44(0)2890 973212
email: mgallay01 at qub.ac.uk
www: www.qub.ac.uk/geog