How can I remove the legend title in ggplot2?

I have a question concerning the legend in ggplot2.

Say I have a hypothetical dataset about mean carrot length for two different colours at two farms:

carrots<-NULL
carrots$Farm<-rep(c("X","Y"),2)
carrots$Type<-rep(c("Orange","Purple"),each=2)
carrots$MeanLength<-c(10,6,4,2)
carrots<-data.frame(carrots)

I make a simple bar plot:

require(ggplot2)
p<-ggplot(carrots,aes(y=MeanLength,x=Farm,fill=Type)) + 
geom_bar(position="dodge") +
opts(legend.position="top")
p

My question is: is there a way to remove the title ('Type') from the legend?

Thanks!