A mature pollen grain of Pinus has

Step-by-step solution

In Pinus, the microspore nucleus divides by a periclinal wall and forms a very small prothallial cell and large central cell. The central cell cuts off a second prothallial cell and antheridial cell. The nucleus of the antheridial cell divides to form generative cell and tube cell. Thus, the pollen grain of Pinus is shed at four cell stage when it consists of two vegetative prothallial cells, a generative cell and a tube cell.