266 MORPHOLOGY. 



More details will be found in the following works : 



Dr. Schimper, Description of Symphytum Zeyheri, &c., in Geiger's 

 Mag. fiir Pharmacie, B. XXIX. p. 1. et seq. 



Dr. A. Braun, Comparative Researches into the Arrangement of the 

 Scales in the Fir Cones, &c. ( Veryl. Unters. ub. die Ordn. der Schup- 

 pen an den Tannenzapfen, fyc.) Nov. Act. Acad. C. L. N. C. T. xiv., 

 vol. i. pp. 195402. 



Dr. Schimper, Essays on the Possibility of a Scientific Comprehension 

 of the Position of Leaves, &c. ( Vortrdge ub. die Moglichkeit eines 

 wissensch. Verstdndnisses der Blattstellung, fyc.) Published by Dr. A. 

 Braun, Flora Jahrg. xviii., No. 10, 11, 12 (1835). 



L. and A. Bravais, Memoires sur la Disposition geometrique des 

 Feuilles et des Inflorescences, precedes d'un Resume des Travaux des 

 MM. Schimper et Braun sur le meme Sujet, par Ch. Martins et A. 

 Bravais. Paris, 1838. 



III. The primary form in which the leaf makes its appearance 

 is, as I have above stated, always that of a little conical body which 

 is pushed out from the axis; its ulterior form depends entirely 

 upon the arrangement of the newly originating, and the expansion 

 of already existing cells, and the leaf is as little confined to a 

 definite circle of forms as any other of the organs, except the seed- 

 bud. It may be globular, ovate, elliptical, and prismatic, as well 

 as filiform, strap-like, and flattened in its expansion, and, by the 

 greater accumulation of the cells in the middle than on the 

 borders, or more flattened mode of expansion in the middle than 

 on the borders, the plane surface may also produce concave forms. 

 The most striking forms of this kind are called pouches (asci), as 

 in Sarracenia, Cephalotus, Utricularia. In all these forms occur the 

 modifications mentioned in the general morphology ; in the plane 

 leaves, especially the divisions and slight indentations of the border. 

 One of the most frequent forms, which is usually laid down as the 

 normal form, is this, the upper part is developed into a plane, the 

 blade of the leaf (lamina), the lower into a filiform part, the petiole 

 or leaf-stalk (petiolus), and in the latter may frequently be dis- 

 tinguished, still lower down, a somewhat thickened or expanded 

 portion, a sheathing portion (pars vaginalis), with which the leaf 

 partly or wholly embraces the axis. This latter portion is fre- 

 quently, especially in compound leaves, swollen into a greater 

 thickness (fleshy), and is then called the cushion (pulvinus) of the 

 leaf or petiole. As a general rule, the flat leaf is so developed that 

 its surfaces look more or less upward and downward, rarely so that 

 its borders have these directions, so that the axis lies in the plane 

 of the leaf, as, for instance, in many New Holland Myrtacece. It 

 is very different from this when a flat leaf of the usual development 

 makes a half turn on its base, so that its surfaces are thus also 

 placed vertically, as, for example, in Lactuca Scariola. One condi- 

 tion, which has already been mentioned when speaking of the axis, 

 occurs also in the leaf, and here becomes of much greater import- 

 ance. A joint (articulatio) is formed rarely (or never?) in the 

 Monocotyledons, frequently in the Dicotyledons, between the leaf 



