Factors modifying the sex ratio inCANNABIS SATIVA L. — Given our lack of knowledge on the effect of age of seed and density of sowing on the sex ratio inCannabis sativaL., over65.000hemp stalks were examined during the years1959–2.These plants were sexually differentiated and were harvested from plots distributed in a randomized block. In each experiment it was found that the number of plants per square meter (which varied from 42,01 to 226,01) did not influence the sex ratio in spite of evident manifestations of natural selection due to this factor. On the contrary, alterations in the sex ratio in favour of the ♀ plants were caused by the age of the seeds, especially if plants obtanied from seeds of the same variety sown in different epochs were compared.