[R] How to transfer variable names to column names?

[Vining, Kelly]

Hello R users,
I have a set of data frames for which I am tallying row numbers, as shown below. 

> nrow(mC_Explant)
[1] 14480
> nrow(mC_Callus)
[1] 23320
> nrow(mC_RegenPlant)
[1] 8108

etc.

I want to create a new data frame which has the variable names as column headings, and then a single row with the nrow tallies. My first step was this:

dfIntron <- c(nrow(mC_Explant), nrow(mC_Callus), nrow(mC_RegenPlant))

Then, to set the column names, I tried this, and got the following error:

 colnames(dfIntron) <- c("mC_Explant", "mC_Callus", "mC_RegenPlant")
Error in `colnames<-`(`*tmp*`, value = c("mC_Explant", "mC_Callus", "mC_RegenPlant" : 
  attempt to set colnames on object with less than two dimensions

Even my first step seems wildly inefficient, and obviously doesn't work. There must be a simple way to do this, but I can't use table(), for example, as there are multiple data frames.

Any help will be appreciated.

--Kelly V.