Abstract: In a flask suitable for tissue or micro-organism culture, having top and bottom walls, a pair of similar side walls, a closed end wall, a second end wall having an opening therein, a tubular open neck in sealing engaged at one end with the second end wall so as to surround the opening therein, and means for sealing the other end of the neck, the improvement which comprises a frangible zone formed on the top wall for access to the interior of the culture flask.