Step 1: Understanding the Problem:
In angiosperms, double fertilization requires the delivery of two male gametes to the female gametophyte.
Because the male gametes are non-motile, they depend on a physical structure to transport them safely through the maternal tissues.
Step 2: Approach and Formula:
Identify the biological terminology based on the anatomical structure used for the transport of the gametes.
The prefix "siphon-" translates to "tube," which directly correlates with the pollen tube mechanism.
Step 3: Detailed Explanation:
The pollen tube acts as a hollow carrier, growing continuously through the stigma and style to enter the ovule.
The specific process of utilizing a hollow tube for the delivery of non-motile male gametes is termed siphonogamy.
The other terms (chalazogamy, porogamy, and mesogamy) refer exclusively to the specific points of entry of the pollen tube into the ovule, not the overarching transport process itself.
Step 4: Final Answer:
The process is correctly called siphonogamy.