Here the 1874 RLDS edition omitted the preposition of, probably accidentally. The 1908 RLDS edition restored it to the RLDS text. Perhaps the lack of the of immediately after the verb gather (“gather together thy flocks”, not “gather together of thy flocks”) led to this deletion of the of after and also. On the opposite side of the question, one could ask whether the original text had the of after and also; in other words, perhaps the of was accidentally added under the influence of several nearby prepositional phrases headed by of (“of every kind” and “of the earth”).
Nonetheless, it makes sense that the Lord would command the Jaredites to gather all their flocks but not all the seed of the earth. They would need to gather only part “of the seed of the earth of every kind”. This same use of the preposition of acting as a partitive marker with the verb gather is found in the King James Bible (in this case, in reference to the gathering of manna):
In other words, no one gathered all the manna. For the same reason, the original partitive reading here in Ether 1:41 is perfectly correct.
Summary: Maintain in Ether 1:41 the preposition of before “the seed of the earth”; the use of the partitive preposition of with the verb gather is expected when referring to the gathering of seed (thus “gather … of the seed of the earth of every kind”).