Why can't i install plugins in subfolder in mu-plugins???

I don’t know why it is, only that it is.

Beside the folder inside “mu-plugins” stick a file with something like the following:

To include a specific file only:

<?php
  $my_plugin = glob( dirname( __FILE__ ) . '/my_plugin_folder/my_plugin.php' );
  include_once( $my_plugin );
?>

or to include a bunch of php files inside the first folder:

<?php
  $my_plugins = glob( dirname( __FILE__ ) . '/my_plugins_folder/*.php');
  if( is_array( $my_plugins ) ) {
  	foreach ( $my_plugins as $my_plugin ) {
  		if( is_file( $my_plugin ) )
  			include_once( $my_plugin );
  	}
  }
?>

@david tx, for the code.

Another question about mu-plugins do the screenshot-x.png have any function? Or is this just for *offline* reference?

i created a file called plugin_folders.php and add

<?php
/********
to include Must Use plugins in folders
********/

//include ds_wp3_menus plugin
$ds_wp3_menus_plugins = glob( dirname( __FILE__ ) . '/menus/*.php');
if( is_array( $ds_wp3_menus_plugins ) ) {
foreach ( $ds_wp3_menus_plugins as $ds_wp3_menus_plugin ) {
	if( is_file( $ds_wp3_menus_plugin ) )
		include_once( $ds_wp3_menus_plugin );
}
}
//include other folder plugin

?>

do the screenshot-x.png have any function? Or is this just for *offline* reference?

As far as I know, those are just for the repo.