These PYREX® flat bottom reusable culture tubes are ideal for plant tissue culture and general culture work. The flat bottom facilitates use with agar slants. Walls and bottoms are of uniform thickness. The tubes are rimless for greater convenience in plugging and rack storage. Optional polypropylene two position closures (Thomas Nos. 9195R55 or 9195R50) can be opened for gas exchange or closed for humidified environment. Internal drip ring minimizes contamination.