| Abstract: | The present paper reports the early development of embryo and endosperm of Paeonia lactiflora. The main conclusions are as follows: 1 The zygote nucleus divides directly to form a coenocytic proembryo with different number of free nuclei. The result confirms the conclusion of Yakovlev[6] as well as Yakovlev and Yoffe[7] On the occurnce of coenocytic proembryo in Paeonia suffruticosa Andr. (P. moutan Sims), P. albiflora Pall. (P. lactiflora Pall), P. officinalis L., P. tenuifolia L., P. anomala L., P. veitchii Lynch (P. beresowskii Komarov), P. wittmanniana, also it agrees with the report of Cave et al.[4] on the occurence of the coenocytie proembryo in Paeonia californica and P. brownii. From the result of our investigation, there is no basis to support Murgai's conclusion obtained in certain species of Paeonia, i.e., the first division of zygote nucleus is accompanied by wall formation and the coenocyte is a suspensor. The primary endosperm nucleus of P. lactiflora divides often earlier than zygote nucleus, or almost at the same time or later in a few cases; 2 Both mitosis and amitosis occur in the free nuclei in the coenocytic proembryo, and mitosis is dominant. In the later stage of development the amitosis occurs at the micropylar region of the coenocytic proembryo, in the free nuclear endosperm at the chalazal region and the appressed part of the chalazal end of the coenocytic proembryo. In addition, in the region of conenocytic proembryo and endosperm polyploid nuclei, irregular nuclei are also frequently met with; 3 Cell wall formation in the coenocyte and the endosperm initiates by means of both cell plate and freely growthing walls, but in the coenocyte wall formation is earlier than in the free nuclear endosperm. At first, wall formation of the coenocytic proembryo begins at the chalazal end, and then extends toward the micropylar region, and in endosperm it begins at the part appressed to the part of the chalazal end of coenocytic proembryo, and then extends toward the chalazal end. We support Cave’s suggestion of the parallel evolution for Paeonia possessed the coenocytic proembryo has no relation to the coenocytic proembryo of the gymnosperms. Further we consider the evolution tendency of the coenocytic proembryo of Paeonia toward a functional specialization. |
