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
The Power of Movement in Plants drew attention to the similarities between animals and plants, e.g., sensitivity to touch (thigmotropism), light sensitivity (phototropism), and gravity (geotropism). Darwin used various methods of enquiry: usually setting up rigorous controlled experiments which are clearly explained in the text, reporting the results and then drawing general conclusions. Studies of nyctinasty were particularly burdensome, to Darwin's rest as well as to the plants: The book is divided into the following chapters, each of which describes types of movements based on Darwin's specific experiments and their results. According to Darwin's son Francis, the book was "widely reviewed and excited much interest among