_For the sake of clearness, however, it has been desirable to sacrifice--with few exceptions--the original order of the passages as written, though it was with much reluctance and only after long hesitation that I resigned myself to this necessity. Nor do I mean to impugn the logical connection of the author's ideas in his MS.; but it will be easily understood that the sequence of disconnected notes, as they occurred to Leonardo and were written down from time to time, might be hardly satisfactory as a systematic arrangement of his principles. The reader will find in the Appendix an exact account of the order of the chapters in the original MS. and from the data there given can restore them at will. As the materials are here arranged, the structure of the tree as regards the growth of the branches comes first_ (394-411) _and then the insertion of the leaves on the stems_ (412-419). _Then follow the laws of Light and Shade as applied, first, to the leaves (420-434), and, secondly, to the whole tree and to groups of trees_ (435-457). _After the remarks on the Light and Shade in landscapes generally_ (458-464), _we find special observations on that of views of towns and buildings_ (465-469). _To the theory of Landscape Painting belong also the passages on the effect of Wind on Trees_ (470-473) _and on the Light and Shade of Clouds_ (474-477), _since we find in these certain comparisons with the effect of Light and Shade on Trees_ (e. g.: _in No._ 476, 4. 5; _and No._ 477, 9. 12). _The chapters given in the Appendix Nos._ 478 _and_ 481 _have hardly any connection with the subjects previously treated._ Classification of trees. 393. TREES. Small, lofty, straggling, thick, that is as to foliage, dark, light, russet, branched at the top; some directed towards the eye, some downwards; with white stems; this transparent in the air, that not; some standing close together, some scattered. The relative thickness of the branches to the trunk (393--396). 394. All the branches of a tree at every stage of its height when put together are equal in thickness to the trunk [below them]. All the branches of a water [course] at every stage of its course, if they are of equal rapidity, are equal to the body of the main stream. 395. Every year when the boughs of a plant [or tree] have made an end of maturing their growth, they will have made, when put together, a thickness equal to that of the main stem; and at every stage of its ramification you will find the thickness of the said main stem; as: _i k_, _g h_, _e f_, _c d_, _a b_, will always be equal to each other; unless the tree is pollard--if so the rule does not hold good. All the branches have a direction which tends to the centre of the tree _m_. [Footnote: The two sketches of leafless trees one above another on the left hand side of Pl. XXVII, No. 1, belong to this passage.] 396.