This exercise makes use of the external files plantgrowth_1.txt, plantgrowth_2.txt and plantgrowth_3.txt, which you can assume are in the working directory. They contain data on the same experiment carried out in three different research centers. Seven research centers still have to send their data. All external data files are tab-delimited and use a comma as a decimal symbol.

Create one data frame plantgrowth which binds all three data files underneath each other. In addition, plantgrowth should contain a column origin containing the name of the file from which the data was read in. In order to help you on your way, we provide the vector files containing the file names.