並列摘要
The sequence of differentiation and maturation of eight different species of ferns (including both eusporangiate and leptosporangiate) are investigated in this report. With the exception of Botrychium and the giant roots of Angiopteris all other roots are protostelic. The numbers of the protoxylem strands range from two to seven. The larger the root diameter, the more the protoxylem poles occur. The endodermis is characterized by a Casparian strip in the roots of Ceratopteris. Angiopteris and Botrychium or is darkly stained in the roots of Adiantum, Osmunda, Pteris and Marsilea. The relationship between the origin of lateral roots and the stele can be summarized as follow: If the pericycle consists of more than one layer of cells, the lateral root initiates from this tissue, e.g., as in Osmunda and Angiopteris; whereas if the pericycle has only one layer of cells, the lateral root is endodermal in origin, e.g., Adiantum, Ceratopteris Marsilea, and Pteris. In roots having diarch or triarch protoxylem, the lateral roots originate opposite the protoxylem, but lateral roots originate between the xylem and the phloem in roots having tetrarch or heptarch protoxylem. The occurrence of sclerenchyma in the cortex is due to genetic factors rather than physiological ones.