Answer:
"Cramming" as used in the given sentence means "filled up so tightly", "packed so full", "stuffed".
Step-by-step explanation:
The word "cram" is a verb that describes or shows tightly packed, or things put together in a compact manner. This verb tells us the manner of how things are kept.
As given in the sentence, the word "cramming" is used to describe how the "substance" grew on the bark of the trees. It details the manner of how they are so densely packed, meaning they are so tightly wounded and stayed together.
Therefore, "cramming" as used in the given sentence means "filled up so tightly", "packed so full", "stuffed".