1. No hybrid plants of Nicotiana tabacum + Petunia hybrida were regenerated from calluses of fusion experiments with mesophyll protoplasts of N. tabacum s, s (2) and v and of P. hybrida mu 1 (2). 2. After in vitro pollination of ovules of N. tabacum with pollen of P. hybrida, filamentous proembryos and cellular endosperms could be detected. But after 8-10 days, embryos and endosperms degenerated completely, indicating a strong zygotic incompatibility of the two genomes. 3. After in vitro pollination of ovules of N. tabacum with pollen of Hyoscyamus niger, large globular embryos and well developed cellular endosperms are found, indicating that the method of in vitro pollination was not the reason for the early degeneration of the tobacco x petunia proembryos. The globular embryos of (tobacco x henbane) hybrids developed further on in a culture of ovules in a special medium 'C'. But then they started to produce callus tissue and did not develop normal seeds as (tobacco x tobacco) in vitro self-pollinations were able to do. 4. After in vitro pollination of ovules of Melandrium album with pollen of N. tabacum, no embryos could be found although several endosperm nuclei could be detected. The hybrid chromosome number was not counted. In Melandrium album, ovules pollinated with P. hybrida divisions of nuclei of the mother plant and the generative nucleus of the father could be photographed. No further development took place.