On both peach and almond trees sometimes spring leaves develop blisters such as you see at the right. Sometimes the blistering is so severe that entire leaves twist and curl so that they hardly look like leaves at all. The disease can even affect flowers, fruits and young twigs. As the season progresses the leaves turn gray and powdery. This powder is the fungus's spores. Eventually the leaves turn brown or yellow and fall off early. Diseased fruits usually have wrinkled areas, are discolored and swollen, lack normal peach fuzz, and fall off early.
Since the species causing the disease, Taphrina deformans, is an Ascomycota, the lifecycle begins with an ascospore. The ascospore itself produces smaller spores by budding. On the leaf surface these spores produce more spores by budding, and when conditions are just right the spores sprout mycelium -- maybe after two spores fuse together. The full story isn't yet known.
The mycelium enters the leaf and works its way among the leaf's cells. At this time, while a lot of complex genetic stuff is going on inside the mycelium cells, something causes the leaf's cells to elongate, causing twisting and blistering of the leaf. Eventually certain cells of the mycelium begin enlarging, growing to such an extent that they cause the leaf's cuticle, or "skin," to burst. Now these special, enlarged mycelium cells work themselves onto the leaf's surface and form a very thin surface called the hymenium consisting of stacked-together, clublike asci. The asci rupture, releasing ascospores, and now the life cycle starts over.
Notice that no "ascus cup" or other complex structure is formed during the lifecycle. This species is regarded as very primitive -- as being a type of fungus that evolved before specialized ascospore-producing structures appeared.