Hint: Chalazogamy is a process of fertilization in which the pollen tube penetrates to the embryo sac through the tissue of the chalaza.
In this question we have asked which of the following plant chalazogamy is found. So, first of all what is Chalazogamy? It is a process of fertilization in which the pollen tube penetrates to the embryo sac through the tissue of the chalaza. Chalaza is the location where the nucellus attaches to the integuments, opposite the micropyle. In contrast to a majority of angiosperms showing porogamous fertilization, several fagalean families such as Betulaceae and Casuarinaceae are known to show chalazogamy, where fertilization is affected by a pollen tube passing through the chalaza instead of the micropyle.
Our first option is casuarina. In Casuarina, fertilization occurs by Chalazogamy. Option B is pistia. Pistia is a genus of aquatic plant in the arum family, Araceae. Pistia reproduces primarily vegetatively by means of daughter plants attached to stolons. The daughter plants have the potential to break off from the parent plant and be moved via water currents or boats to start new populations. It can also reproduce sexually via seeds. Next option is pisum. For fertilisation in pisum, pollen has to be transferred to the stigma of a flower: a process known as pollination. In pisum double fertilisation also occurs. Double fertilization is a complex fertilization mechanism of flowering plants. This process involves the joining of a female gametophyte with two male gametes. Next option is cucurbits. Endogamy occurs in cucurbita. Mesogamy means when the pollen tube enters through the integuments or through funiculus. So, chalazogamy occurs in casuarinas and the correct option is A.
The correct option is, A - Casuarina.
Note: In chalazogamy, the pollen tube grows discontinuously from the stigma to ovules in about 3 months. At the time of pollination, the ovules have not yet formed in the ovary, and require a long time to develop. The pollen tubes lie in a zigzag line and are branched in the upper region of the style, and their growth is arrested there until the ovary develops further. So, it was a very long process. Chalazogamy is very rare. It is found in Casuarina, Juglans, Betula, etc. Which is closely related to casuarinaceae.