Massachusetts Constitution Pt. 2, Ch. II, § 1, Art. 5

ART. V. The governor, with advice of council, shall have full power and authority, during the session of the general court to adjourn or prorogue the same to any time the two houses shall desire; [and to dissolve the same on the day next preceding the last Wednesday in May;] and, in the recess of the said court, to prorogue the same from time to time, not exceeding ninety days in any one recess; and to call it together sooner than the time to which it may be adjourned or prorogued, if the welfare of the commonwealth shall require the same: and in case of any infectious distemper prevailing in the place where the said court is next at any time to convene, or any other cause happening whereby danger may arise to the health or lives of the members from their attendance, he may direct the session to be held at some other, the most convenient place within the state.

[And the governor shall dissolve the said general court on the day next preceding the last Wednesday in May.]