The size of an esrog, Reb Meir say it must be at least the size of a nut,Reb Yehuda says the size of an egg. The maximum, Reb Yehuda says is you can hold two in one hand, Reb Yossie says even one two hands.

Succa 3:8

Reb Yehuda says you can only bind a lulav with its own species, Reb Meir says even with a string. There was a story with the people of Yerushlayim that they used to bind their lulavas with strings of gold. Reb Yehuda says that it was bound with their species under the gold.