The pollen grain has two layers-outer exine and inner intine. Exine is made up of highly resistant sporopollenin while intine is pectocellulosic. At certain places exine is thin or absent called germpore or germinal furrow. After reaching on stigma the pollen grain absorbs water and nutrients from the stigmatic secretion through its germ pore. The tube or vegetative cell enlarges. It comes out of the pollen grain through one of the germ pores or germinal furrows to form a pollen tube.