You can, but you get uneven lighting in good situations, and in worst case, since LEDS (or any given diode) are not perfect systems, variations in them will cause one led to conduct more current then the rest. Eventually it will burn out before the rest, which would lead to the same current to be divided by a smaller amount of imperfect diodes, which would lead to (rinse, lather, repeat).

See Why exactly can't a single resistor be used for many parallel LEDs? for more info.

You can, but you get uneven lighting in good situations, and in worst case, since LEDS (or any given diode) are not perfect systems, variations in them will cause one led to conduct more current then the rest. Eventually it will burn out before the rest, which would lead to the same current to be divided by a smaller amount of imperfect diodes, which would lead to (rinse, lather, repeat).

See Why exactly can't a single resistor be used for many parallel LEDs? for more info.