作 者 ：XING Shu-Ping, CHEN Zhi-Duan, LU An-Ming
期 刊 ：植物分类学报 1998年 5期
Keywords:Ostrya virginiana, Systematic significance,
Abstract:
The development of ovules and embryo sacs in Ostrya virginiana was studied for
the first time. Most ovaries had two ovules which were anatropous, unitegmic and crassinu-
cellate. The ovule usually possessed several archesporial ceils which divided periclinally into
the upper parietal cell and the lower sporogenous cell. The sporogenous cell functioned di-
rectly as megaspore mother cell. The tetrad of megaspores was linear in arrangement, and
every megaspore might be functional. One ovule often contained 2- 6 embryo sacs and the
embryo sac belongs to Polygonum type. It can be concluded from the present data that all
ovules among the genera of the Betulaceae are unitegrnic. There are more groups with the
phenomenon of multiple embryo sacs in anemophic plants such as Betulaceae, Casuarinaceae,
Graminae, Jnglandaceae, Myricaceae, Simaroubaceae, Ulmaceae, than in entomophilous
plants. Multiple embryo sacs also occur among some parasitic plants and saprophytes, e.g.
Orobanchaceae, Cassytha in Lauraceae, Cuscuta in Convolvulaceae and Utricularia in Len-
tibulariaceae. It may be inferred that the characteristic of multiple embryo sacs be an evolu-
tionary adaptation of those plants with lower pollination rate to increase the rate of fertiliza-
tion. Finally, a comparison of embryological characters among the genera of the Betulaceae
shows that the family is of a number of common embryological characters, such as multicellu-
lar archesporium, multiple embryo sacs in one ovule, and a long interval between pollination
and fertilization. The diversity and systematic significance of several embryological characters
among the “higher” hamamelid families are also discussed. It is still hard to explain the phy-
logenetic relationships among those families clearly only with.