The use of the half-tone block is now almost universal, so that it is hardly necessary to mention examples, more especially as they are hard to judge without seeing the original picture. Those in the present book are all of a high quality. Excellent examples will also be found in Tansley's _Types of British Vegetation_ (Cambridge, 1911) and in the _Journal of the Royal Horticultural Society_. Proofs should be carefully compared with the originals, particular attention being paid to the rendering of the tones; as already remarked, fine etching will clear up a block and will often prove a remedy to flatness. An author will naturally consider whether a photograph is to be reproduced by means of photogravure, collotype or half-tone. It is impossible to lay down any laws on the subject, but the following points should be considered. If it is essential to have the reproduction in the text, a half-tone block must be used; it must, however, be remembered that the paper used for the letterpress may be very unsuited for the printing of half-tones. On the other hand, if it be immaterial where the picture is placed, then the relative merits of photogravure, collotype and kindred processes and half-tone must be weighed. Provided that expense need not be considered, photogravure will, in the majority of cases, give the best results; on the other hand, if this process is too costly, then the choice lies between collotype and half-tone. The latter method will often give a result with more contrast as compared with collotype, whilst collotype will give a truer interpretation of the tones. As has already been remarked, the best results with half-tone blocks only are to be obtained by the employment of a paper which seemingly has no lasting qualities; it therefore follows that if the reproduction forms an important record, the use of collotype is indicated, since many varieties of good paper are available. As a general rule photo-micrographs are best reproduced by collotype. In order that the respective qualities of these three processes--photogravure, collotype and half-tone--may be compared, Plates 8, 9, and 10 have been made from the same photograph, a view taken by Dr. F. F. Blackman of the Bouche d'Erquy, a salt marsh in Brittany, which was selected chiefly on account of the large number of tones it contains. [Illustration: PLATE 8. Photogravure] [Illustration: PLATE 9. Collotype] [Illustration: PLATE 10. Half Tone] These three plates are not entirely comparable, since the heavy shadows in the right hand bottom portion of the photogravure have been touched up by the engraver. This was not intended by the author, but the plate was retained as it shews that directions regarding this point should not be omitted when sending the drawing or photograph to be reproduced. It also indicates that for critical work, when an exact a facsimile as possible is required, collotype should be used, for the plate cannot be touched up.