Whats actually happening is that the hashes are flattened into a list, then this list is assigned to a new hash. So, %h1 and %h4 wind up with the same contents below:

#!/usr/bin/perl -wT
use strict;

my @a1 = ('jan','January','feb','February');
my @a2 = ('mar','March',  'apr','April');
my %h1 = (@a1, @a2);                         # Two arrays become one h
+ash

my %h2 = ('jan','January','feb','February');
my %h3 = ('mar'=>'March' ,'apr'=>'April');   # '=>' is really just a c
+omma

my %h4 = (%h2,%h3);                          # Hashes get flattened an
+d behave
                                             # nearly the same as the 
+two
                                             # arrays did above

print "h1\n";
print "\t$_ => $h1{$_}\n" for (sort keys %h1);

print "h4\n";
print "\t$_ => $h4{$_}\n" for (sort keys %h4);

=OUTPUT
h1
        apr => April
        feb => February
        jan => January
        mar => March
h4
        apr => April
        feb => February
        jan => January
        mar => March
[download]

-Blake