Final answer:
Frank would most likely call the part of the vine that grew into the brick 'roots', as these are parts of the plant responsible for anchorage and absorption.
Step-by-step explanation:
A horticulturist like Frank, observing vines that have grown into the brick, would most likely refer to the part of the vine that grew into the brick as the roots. This is because the roots are the part of a plant that typically grow into surfaces for anchorage and are responsible for absorbing water and minerals. Unlike leaves, stems, or flowers which have different functions such as photosynthesis, support, and reproduction, it is the roots that anchor the plant and can penetrate structures like bricks, which would make them difficult to remove.
Moreover, roots can exhibit indeterminate growth, which means they continue to grow throughout a plant's life, allowing them to eventually work their way into cracks in the brickwork. The roots can also form specialized structures like aerial roots in certain cases, or become modified for additional support. For example, certain types of ivy have root-like structures with adhesive pads that allow them to cling to surfaces. These specialized roots are what allow the vine to stabilize itself on vertical surfaces like the side of a house.