Plotting a histogram does not come around

I am trying to plot a histogram, but the figure that results does not quite come round to me.

if true
   load('iris_data.csv')  %after addpath, I need to parametrize this somehow
   plot(std(iris_data))  % can I change the default filename or do I have to use another variable as a matrix. 
   histogram(std(iris_data));
end

Data set - http://archive.ics.uci.edu/ml/datasets/Iris.

I wonder if there is a document indicating all the data structures possible within MATLab.