Studies On Morphogenesis And Comparative Morphology Of Ginkgo Biloba Var. Epiphylla Mak.

Morphogenesis and comparative morphology of Ginkgo biloba var. epiphylla Mak. in Yiyuan county, which is the first one in China,was researched, using the plant sectioning technique and plant chromosome technique. Micromorphological research of both normal seeds and epiphyllous seeds in 6 individuals of Ginkgo biloba var. epiphylla was conducted. The results obtained were as follows:(1) The leaf of Ginkgo biloba var. epiphylla can be separated into normal leaf and leaf with epiphyllous ovules. The occurrence rate of anastomoses is 14.2%. The vein of normal leaf can be separated into four types according to anastomoses, i.e. closed type, W type, V+W type and double V+W type. And that of leaf with epiphyllous ovule was classified into three types, i.e. uni-arcuate, biarcuate and mutli-arcuate type. In addition, there were variegated leaves in the tree. The stomatas of Ginkgo biloba var. epiphylla were amphistomatic, the stomatal apparatus was monocytic. There were difference between normal leaves and leaves with epiphyllous ovules on leaf length, leaf width, leaf fresh weight, leaf area.(2) The mesophyll of normal leaf blades had the differentiation of palisade tissue and spongy tissue, but the mesophyll of lamina with epiphyllous ovules was composed by the homeotypic parenchyma cells. There were ridges on the lamina with epiphyllous ovule and the mesophyll cells in ridges were composed by large parenchyma cells. The location of their veins was divided into two types, i.e. distributing at the both sides of the ridge type and distributing just above the ridge type. Moreover, the veins in ridges were denser than that of normal sites. 3 to 4 layers lignified cells located at the lateral border of phloem, in the ground tissue of the petiole of the leaf with epiphyllous ovule, which was reported for the first time.(3) The multi-ovule occurrence rate was higher and the pattern of multi-ovule was more in Ginkgo biloba var. epiphylla than that in normal Ginkgo tree, which indicated that Ginkgo biloba var. epiphylla was primitive. The research on multi-ovule confirmed that the evolutionary trend of reproductive organ of Ginkgo is that the decrease of ovules number in stalk, the increase of ovule size, the disappearance of stalklet. The vascular bundle is outside phloem type, there were albuminous cells surrounded the phloem. The secretory cavity is marginal growing type. The secretory cavity was distributed in integument, and the formation and developmental pattern of the secretory cavity was schizolysigeneous. There were stoma in normal ovule and stalklet, and the morphology of stoma is identical to that in the leaf. In this research, two stomas and three stomas that close to each other were firstly observed in the normal ovule and stalklet. The chromosome number of female gametophyte of normal ovule in Ginkgo biloba var. epiphylla was 24.(4) The occurrence rate of epiphyllous ovules in early stage is less than 20%, while the occurrence rate of epiphyllous seed was lower than 5%. The development of epiphyllous ovules on the leaf comprised initial stage, formation stage, expansion stage and mature stage. At initial stage, a slender ridge, whose base end located between veins and top end produced a lobe, was produced in the leaf with epiphyllous ovule. And, the epiphyllous ovule is developed from proximal to marginal. Generally, the abaxial surface of ridge was more apparent than that of adaxial surface. There was no differentiation of palisade tissue and spongy parenchyma. There was a great many of large parenchyma in the ridge. The epiphyllous ovule probably originated from the dedifferentiation and redifferentiation of these cells. The differentiation of nucellus and integument of epiphyllous ovule is at middle May. Micropyle and collar were also observed in the epiphyllous ovule, but there was no pollen chamber.(5) There was heterochrony on development of epiphyllous ovule. The heterochrony was exhibited in two aspects, i.e. compared to normal ovule, the epiphyllous ovule lag behind, another aspect is that among epiphyllous ovules, there was heterochrony. The leaf with epiphyllous ovule is smaller than normal leaf, and the leaf can be divided into five types, i.e. unilobed solitary type, unilobed clustered type, bilobed clustered type, multilobed solitary type and adsperse type. Great variation of both normal seed and epiphyllous seed was also noticed. The short shoot producing epiphyllous ovule is alternate, intermittent. (6) The sclerotesta of normal seed in 6 individuals of Ginkgo biloba var. epiphylla consist of tracheid with bordered pit. However, difference was noticed between epihyllous ovules. There were two types of tracheid, i.e. tracheid with bordered pit and spiral tracheid in the sclerotesta of Ginkgo biloba var. epiphylla in Zhinüdong, Zhongzhuang, Jinan, Tain, but there was only tracheid with bordered pit in both normal seed and epiphyllous seed sclerotesta of Ginkgo biloba var. epiphylla in Youfang and Baiyu. In addition, difference was also observed in endotesta.In the paper, the phylogeny of Ginkgo biloba var. epiphylla was discussed, including the morphological essence of female reproductive organ, relationship of Ginkgo, and occurrence mechanism of Ginkgo biloba var. epiphylla. This research is of great importance to probe the phylogeny of Ginkgo biloba.