Figure 3.3–Longitudinal sections through ovaries of flowers (A) and developing fruit (B-F) of Arceuthobium cyanocarpum (A-D) and A. americanum (E,F). A: mamelon (m) with 2 embryo sacs (g) and fruit wall (f), x100. B: cellular endosperm (en) in mamelon (m), x100. C: same specimen as B but at a different focal plane, embryo (e), mamelon (m), and fruit wall (f), x100. D: enlarged view of specimen seen in C showing two-celled embryo (e) and endosperm (en), x250. E: globular embryo (e) in endosperm (en), note crushed mamelon (cm), x100. F: same development stage as E, but with necrotic, aborted embryo (n) surrounded by necrotic endosperm and fruit wall (f), x100. (C. L. Calvin)