The last one I believe.
An excerpt from a website I found:
Plant Hybridization Experiments
Gregor Mendel conducted hybridization experiments on around 29,000 pea plants. Peas were an ideal choice for Mendel to use because they had easily observable traits there were 7 of which he could manipulate. He began his experiments on peas with two conditions. The conditions were 1) possess constant differentiating characteristics and 2) hybrids of such plants, during flowering period, be protected from the influence of all foreign pollen.[8] The second condition was used to protect from an accidental impregnation thus would cause misleading results. Mendel planned to selectively cross pollinate the peas with one another to study the traits passed on and the results from each pollination. He acquired about 34 varieties of peas and chose 22 different types to conduct his experiments with which varied in color and size.[8] He took years of breeding constant family lines to perfect the original constant traits. Mendel used seven pea plant traits in his experiments which include flower color (purple or white), flower position (axil or terminal), stem length (long or short), seed shape (round or wrinkled), seed color (yellow or green), pod shape (inflated or constricted), and pod color (yellow or green). The first generation of the hybrids produced a 3:1 ratio where there were 3 plants showing dominant traits and 1 showing recessive.[8] The second generation produces a 2:1:1 ratio. This showed there was one with the recessive trait, two with hybrid trait and one with dominant trait.
(SOURCE: https://sites.google.com/a/wisc.edu/ils202fall11/home/student-wikis/group8)
