A Study On The Anatomy Of Fern Sporangium And Its Relationship To The Leaf Vein

As the sexual reproduction organs, the morphology of sporangia could show the evolution between each group of ferns. As the earliest vascular plants, with the evolution of sporangia, the relationship between sporangia and veins have changed and the soral vascular appeared. We observed the morphological changes of sporangia in many fern groups by the microscope, and discussed it in the fern phylogeny and taxonomy. We also researched the relationships between the sporangia and veins by the paraffin embedding method, and discussed the development of soral vascular. The results as the follows:1. Morphology of sporangiaThere are five types of annulus:no annulus type, apical annulus, lateral annulus, oblique annulus, vertical annulus. The open of sporangia is vertical in the no annulus type and apical annulus type, and have no ability to eject the spores in these two types. The open of lateral annulus type is also vertical, but the sporangia in Diplopterygium chinense could eject the spores, while the Osmunda claytoniana could not. The sporangia in types of oblique annulus and vertical annulus are lateral open, and except some special species, all of these types can eject the spores. According to the morphology of these five types of annulus, we can infer the evolvement rule of sporangia:no annulus type to apical annulus, to lateral annulus, to oblique annulus, to vertical annulus.The cell numbers of annulus are not the same in different species, and even in the same species. It is very usefull in the taxonomy of ferns. On the overall level, the cell numbers are less in the families of Polypodiaceae.The length of the stalk is also not the same in difference species. The shortest stalk is very close to the leaves. The longest stalk is almost2-3times to the capsule. On the overall level, the longest stalks are the species in Polypodiaceae. The length of the stalk maybe has something to do with the size of sori and the density of sporangia.The distance of annulus to the stalk is not the same as well in difference species. The distance could have something to do with the ejection efficiency of sporangia.The stomium is related to the open of sporangia. The stomium is diffrent in the columns and the morphology. Most species have one column of stomium. Small parts of the species have one or two. And the lip cell is more flat in primitive species, while in evolutionary species, the stomium is protruding.In primitive species, the cell wall of the capsule is more and small, and the shape is more regular. While in evolutionary species, which is less and more unregular.2. The relationship of sporangia and leaf veinThe growths of sporangia are related to the vascular. Some grow on the leaf veins directly and have not caused the veins Changed. And some are also grow on the leaf veins directly but have caused the veins changed. There are other taxa that the sporangia do not directly grow on the veins, but on the soral vascular that connects to the leaf veins.The soral vascular is a complicated vascular system that could be thought to be a differentiation of leaf vascular system. So it could be taken for an advanced feature. It is stabilized in the same genus and it maybe the same in different genera. So it could be very usefull in the phylogeny and classification.