Final answer:
In tropical rainforest trees, cotyledons function either as storage or absorptive organs. Storage cotyledons hold nutrients, while absorptive cotyledons take up and transfer nutrients from the endosperm to the embryo. These functional differences prevail among various angiosperms, including both monocots and dicots.
Step-by-step explanation:
The two contrasting functional forms of cotyledons found in tropical rainforest trees are storage and absorptive. In many dicot angiosperms, cotyledons serve as a storage for nutrients during the development of the seed. These cotyledons can grow large and store substantial materials, often taking up most of the seed volume as seen in crop species. Alternatively, in some plants, including monocots, the single cotyledon known as a scutellum acts mainly as an absorptive organ. It absorbs nutrients from the degraded storage tissues, such as the endosperm, and transfers these nutrients to the developing embryo through vascular connections.
Certain dicot species have cotyledons that also absorb nutrients from the endosperm during germination, though other dicots may not have endosperm at all, storing the nutrients directly in the cotyledons themselves. Tobacco, tomato, and pepper are examples of endospermic dicots with absorptive cotyledons, while the peanut and split pea exemplify non-endospermic dicots with storage cotyledons.