Development of the ovule and macrogametophyte are similar, except for minor differences, in Monarda fistulosa, M. didyma, M. punctata, and Nepeta cataria. The ovule is anatropous, has a single massive integument, a one-layered nucellus which does not persist, a hypostase tissue, and an integumentary "tapetum." 2. The chalazal macrospore is the functional one and the embryo sac is of the common seven-celled type. M. fistulosa has the largest macrospores. 3. An obturator is developed in all but N. cataria. 4. The integument incloses the nucellus later in M. punctata than in the other species. It is thicker in M. didyma and M. punctata than in M. fistulosa and N. cataria. 5. The hypostase is very prominent in M. fistulosa, rather prominent in M. didyma and N. cataria, and not so conspicuous in M. punctata.
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Elizabeth P. Bushnell (1936) studied this question.