Consider the following statements and choose the correct answer:
1. In angiosperms the pollination consists of transference of the pollen grains from the anther to the stigma either by self-pollination or by cross-pollination
2. Pollen grain is shed from the pollen sac in the two-celled stage
3. The exine of each microspore grows out into a tube, called the pollen tube
4. The growth of pollen tube is stimulated by sugary substances secreted by the stigma