At the time of pollination, tube nucleus is present, i.e. the pollen grain is usually 3-celled (tube cell + two male gametes). the tube nucleus degenerate when the pollen tube enters the ovary. So, at the time of entering into ovule, the pollen tube has 2 male nuclei.

Explanation:
The pollen tube is a long and slender structure that develops from the pollen grain after it lands on the stigma of the flower. It plays a crucial role in the process of fertilization by delivering the male gametes to the female reproductive structures of the flower, known as ovules.

Structure of the Pollen Tube:
The pollen tube consists of several important components that aid in its growth and function. These components include:
1. Tube Cell: The tube cell is the main body of the pollen tube. It contains a large nucleus and cytoplasm that provide the necessary nutrients and energy for the growth of the tube.
2. Generative Cell: The generative cell is located within the tube cell. It is responsible for producing the male gametes, also known as sperm cells.
3. Vegetative Cell: The vegetative cell is located at the tip of the pollen tube. It helps in guiding the tube towards the ovule and provides structural support to the growing pollen tube.

Process of Fertilization:
The pollen tube grows through the style of the flower towards the ovule. Once it reaches the ovule, it enters through an opening called the micropyle. The pollen tube then releases the male gametes into the ovule, where fertilization takes place.

Number of Male Nuclei in the Pollen Tube:
At the time of entering the ovule, the pollen tube contains two male nuclei. These nuclei are produced by the division of the generative cell within the tube cell. One of the male nuclei fuses with the egg cell present in the ovule to form a zygote, which develops into an embryo. The other male nucleus fuses with the two polar nuclei in the ovule to form endosperm, which provides nourishment to the developing embryo.

Conclusion:
In conclusion, the pollen tube contains two male nuclei at the time of entering the ovule. These nuclei play a vital role in fertilization by fusing with the egg cell and polar nuclei to form the zygote and endosperm, respectively.

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