The preparation of the First Edition was an experiment, as there was some doubt as to the demand for such a book and considerable uncertainty as to how many people would be able to use it successfully. The sales of the First Edition have proved conclusively the demand for a book of this kind, and it has also been proved that the hand-lens can be successfully used to determine a much larger number of mosses than was included in the First Edition. This is shown by the readiness with which persons of no special scientific training have identified the common mosses by its use.<br><br>By the use of slides prepared as for the compound microscope, and the very best lenses such as are advertised in the last pages of this book many characters which were little or not at all used in the First Edition can be utilized in determining difficult species. Such characters are the gross structure of the peristome, the characters of the costa, and the margins of the leaves, position of the reproductive organs, and in many cases the general outline of the cells.<br><br>The hand-lens can never equal the compound microscope for making out these finer details of structure, but the compound microscope is beyond the reach of many who would gladly study the mosses if it can be done with a hand-lens. No characters have been utilized which the author has not been able to make out with his lens, but it may easily be true that the beginner may not be able to see as much at first. The author believes that the limit of utility of the hand-lens has been reached in this edition, so far as the mosses are concerned at least. The section on the Hepatics is less complete owing to the limitations of the author.