Russian Garmon (garmoshka) is a traditional reed music instrument with bellows and two push-button keyboards. The left keyboard is intended for accompaniment: by pressing a button one makes bass or an entire chord sound. The right keyboard is for playing the melody.

Garmon appeared in Russia somewhat in the first half of the 18th century.

Russian masters started to perfect the Viennese diatonic Garmon in the 1st quarter of the 19th century; it led to creation of the then most widespread two-row Garmon of "Russian" and "German" systems. The pitch of a sound played by pressing a key (button) depended on the direction of the bellows movement, i.e. one and the same button gave sounds of different pitch while compressing and while releasing.

Varieties of garmons created by Russian masters at that time were named after the places of their invention or manufacturing (Tula, Saratov, Tatar, Lebanese, and Cherepovets garmoshkas, etc.). Many of these accordions were adapted for the temperament of Russian, Tatar, Mari and other folk songs.

In the process of further development of Garmon Russian masters created a chromatic two-row diatonic Garmon, with the pitch not depending on the direction of the bellows’ movement.

As the pitch in Viennese Garmon of all versions of tuning system changes depending on the direction of the bellows’ movement, its range is almost 1,5 times more than the range of chromatic Garmon with the same number of keys. But along with this advantage Viennese Garmon has an essential drawback - it is much more difficult to play. Therefore Viennese Garmon has been gradually passing out of use, and playing it nowadays is already extremely limited. As for the diatonic chromatic garmon, due to its limited performing abilities since the 1970s it has stopped meeting heightened cultural requirements of performers and has been used more and more seldom.

Diatonic chromatic Garmon with 25 keys (buttons) for melody (the right hand) and 25 buttons for basses or accompaniment (the left hand) is the most widespread type now.

By the idea of N.Beloborodov (1828-1912) the first chromatic two-row Garmon was created in 1870. As for the Russian three-row chromatic Garmon created by master P. Sterligov in Petersburg in the late 19th – early 20th cc garmonist A.Orlanskiy-Titarenko (1877-1941) named Bayan after the Old Russian singer-poet mentioned in The Song of Igor's Campaign.

Perfection of this instrument in Russia has led to creation of three basic versions of bayans: the ones with ready accompaniment (fixed chords - major and minor triads and seventh chords), with elective accompaniment (the performer plays the necessary chords) and with ready-elective accompaniment (combining fixed and elective chords).

The latter version of bayan is the most comfortable one, though it is more complicated to play than bayan with ready accompaniment.

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Sources:
    Russian Wiki
    accordion-nt.spb.ru