Fern fern ("Onoclea sensibilis"). Giant water fern ("Salvinia molesta") is one of the world's worst aquatic weeds. The important fossil fuel coal consists of the remains of primitive plants, including ferns. Ferns have been studied and found to be useful in the removal of heavy metals, especially arsenic, from the soil. Other ferns with some economic significance include: The study of ferns and other pteridophytes is called pteridology. A pteridologist is a specialist in the study of pteridophytes in a broader sense that includes the more distantly related lycophytes. Pteridomania is a term for the Victorian era craze of fern collecting
Four Treasures of the Study ceramic stones (澄泥硯) which are manufactured by a process which is said to have been developed in Luoyang in Henan. Classical scholars had more than just the Four treasures in their studies. The other "Treasures" include the brush-holder (笔架), brush-hanger (笔挂), paperweights (镇纸), the brush-rinsing pot (笔洗), and the seal (圖章) and seal-ink (印泥). For painting, Chinese pigments are also used. Four Treasures of the Study Four Treasures of the Study, Four Jewels of the Study or Four Friends of the Study is an expression used to denote the brush, ink, paper and ink stone used in Chinese and other