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A- embryo
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A- egg cell
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A- sperm cell
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The answer to your rather difficult question is paper. only certain trees make gum rubber, only certain trees make syrup and none of them make turpentine( an extremely flammable substance. the only thing you can get from almost every tree is paper.
The reason as to why fungi fossils seem so rare is that they are usually microscopic and often difficult or impossible to identify.
Not much information on fungi fossils has been documented. This could be because fungi fruiting bodies consist of soft, fleshy and easily degradable tissues which due to their poor integrity do not keep or preserve as well as animal tissue.
Even when available, it takes a trained eye to recognize fungal fossils. Not many people have the training and expertise to recognize the fossils.