Many plant species exist as separate male- and female plants. How do they propagate from the seed?

Question

In species that exist as separate male- and female plants, presumably the pollen will come from the male plant, while the seed will develop in the female plant. How can this seed coming from the same female plant develop in separate male- and female plants?
I can see 2 possibilties:
1.
The female flower produces both male- and female seeds. If so, what causes the differentiation between those two kinds of seed, when they develop in the female plant?
2.
The female plant makes only one type of seed that differentiates in male- and female plants only after germination. If so, what causes this differentiation?

Which of these 2 is the right answer?

Louis Harmsen

Answer 1

It all comes down to sex chromosomes...like when male and female animals mate, some are male and others are female. Same principle except these are plants.

Answer 2

I'll go with the other two on the chromosome side.

There aren't many of these dioecious plants, and they tend to be trees or shrubs. Holly is one.

Answer 3

#1 is mostly right. Its like people, two sexes.