Mr LEAF. 



when UM WWM form* of UM *xi* do not interfere. Compare but 

 UM rmtll of leave* of cVaeei > ferforam, the stalk of Liliom 

 Jf_tJjin, a shoot of />?/ Jilalala, a eon* of jlW em/M, and 

 UM (rait peduncl* of I/tita*iui ainmm, which latter exhibits the 

 of UM leave* *ven through iu fruit which originate 



LEAF. 



S8 



On this subject UM student should consult the following work* : 

 Dr. Schimper. ' Description of Symph t turn Zeyberi,' Ac., in ' Oeiger's 



May. fur Phannaci*.' b, jxlx. p. L et sea. 



Dr. A. Brsun, 'Comparative Researches into the Arrangement of 



Un Seal** in the Fir Cone*,' Ac. Nov. Act Acad. C. L. N. C. T. xiv., 



Dr. Schimper. ' Kasays on the Possibility of a Scientific Compre- 

 hension of UM Position of Leave*,' Ac. Published by Dr. A. Braun, 

 Flora Jahrg.' xviiL, No, 10. 11, U (1885). 



L. and A. Bravaia, Memoirr* sur U Disposition goomttrique des 

 Fruille* et des Inflorescences, preceVl^* d'un lU<uuu< de* Travaux de* 

 MM. Bchimper et Braun snr le meme Snjet, par Ch. Martin* et A. 

 Bravaia.' Paria, IMS. 



The primary form in which the leaf makes its appearance is, as 

 above stated, always that of a little conical body which is pushed out 

 from the axis ; iu ulterior form depending entirely upon the arrange- 

 ment of the new cells, and the expansion of already existing cells, and 

 the leaf i* aa little confined to a definite circle of forms as any other of 

 UM organ*, except the ovule or seed-bud. It may be globular, ovate, 

 elliptical, and prismatic, a* well a* filiform, strap-like, and flattened in 

 Ha expansion, and, by the greater accumulation of the cells in the 

 middle than on the border*, or more flattened mode of expansion in 

 UM middle than on the border*, the plane surface may also produce 

 concav* forma. The most striking forms of this kind are called 

 Pouche* (Aid), a* in Sarractnia, CejJiolotut, and L'lricviario. One 

 of UM most frequent forma, which i* usually laid down as the normal 

 form, i* this the upper part U developed into a plane, the Blade 

 of the Leaf (Lamina), the lower into a filiform part, the Petiole 

 or LeafStalk (Petiolus), and in the latter may frequently be du- 

 i r| ,..i^^ | (till lower down, a somewhat thickened or expanded 

 portion, a Sheathing Portion (Pars Vaginalia), with which the leaf 

 partly or wholly embrace* the axia. This latter portion is fre- 

 quently, especially in compound leave*, swollen into a greater 

 thickneas (fleshy), and i* then called the Cushion (Pulvinus) of the 

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

 iu ratface* look more or leas upward and downward, rarely so that 

 iu bonier* have these direction*, so that the axia lies in the plane of 

 UM leaf, as, for instance, in many Australian tfyrtacta. It is very 

 different from this when a flat leaf of the usual development makes a 

 half torn on iu baa*, so that it* surface* an thus alto placed verti- 

 cally, aa, for example, in Laetnea Srariola. One condition, which has 

 already been nisnUoaiii when (peaking of the axis, occurs also in the 

 leaf, and here become* of much greater importance. A Joint (Articu- 

 laUo) i* formed rarely (or never f) in the Monocotyledons, frequently 

 in the Dicotyledon*, between the leaf and the axia, in consequence 

 of which the leaf is, after a certain time, thrown off from the axis, 

 whO* in other case, it gradually die* and decays on the axis iUelf. 

 Thai true articulation is often repeated in the continuity of one and 

 the earn* leaf, cither only *o that a joint U formed U t ween the petiole 

 and th* lamina (for example, in Cttrui, IHontra), or in such a manner 

 that in the flat Subdivided Leave* (Folia Pinnatuecta, Palmatiaecte, 

 Ac.), every lob* i* connected to the main body by a joint These 

 latter are called Compound Leave* (Folia Composite), and, according 

 to the subdiviaion. Digitate, or Pinnate (Folia Digitata, Pinnate, Ac.). 

 The erparate part* are named LrafleU (FolioU), and the part con- 

 necting all then i* UM Common Petiole (Petiolus Commuuis). The 

 Uaflete can of conn* aerom* all th* forms of the leaf, in particular 

 they may b* again separated into lamina, petiole, and pulvimu. In 

 OOM Australian acacia* (for instance, Acacia kettntpkylla) the first 

 leave* are compound ; they gradually form fewer and fewer leaflet*. 

 till at last the part corresponding to the common petiole alone remains, 

 which then appear* a* a perpendicular plate, and i* called a Pbyllodium, 

 to ifclsH"!'" it from the other perfect leave* of the same plant 



The pooches or pitoben which occur in Xtpnlktt, Sarracenia, 

 tVpJUfarfu, IX**idi* Kafitnana and D. cfcw/o, Martgravia, Norantta, 

 I'trmlaria, Ac , are not yet perfectly understood. The pouche* 

 apparently present three different type* : 1. In ftarractnia it i* the 

 lower part of th* leaf which exhibit* a form resembling a cornucopia, 

 whil* at the apper border ran* oat a flat expansion (the lamina of the 

 leaf), etparated from the pooch by a deep InoWon on each pi.ie. The 

 lower half of UM internal surface of the pouch i* clothed with bain 

 directed downward*; the upper part I* smooth. In Ntpenlket a 



j little papilla- of very 



cellular tissue, while above the epidermis project* 

 down over UM** like the raves of a boos*. In both the cavity is 

 faTBied from UM leaf in such a manner that the closed base of the 

 pooch eamsoond* to the baa* of the leaf (Sarratnia). or lie* quite 

 ctos* to H (ArsotfAo). In Duckidi* AoJtenaM and D. c/aro/o, on 

 UM contrary, UM opening of UM pouch U turned towards the bat* of 



the leaf. Cepkalotut appears to possess a structure similar to that of 

 Sorracotio. In all the plants mentioned the pouch constitute* the 

 main body of the leaf. 2. In ifareyratia and Xoranlca, on the other 

 baud, according to Limlley, the pouches are formed by the stipules. 

 3. In L'lricularia many separate portions of the divided leaf unite to 

 assume a very complicated form of pouch. Originally these form a 

 little shortly-stalked somewhat cornet-shaped body in the angles of 

 the divisions of the leave*. In this little body are especially developed 

 the under side and the inner border of the orifice (which does not 

 increase much in size), so that the full-grown pouch present* itself aa 

 a roundish and somewhat laterally-compressed body, which above U 

 continuous by one angle with the stem, while the other exhibiu an 

 orifice, which forms a little funnel projecting inwards. The external 

 orifice of this funnel is closed by a kind of beard growing on the 

 upper border ; the lower part of the internal surface of the funnel 

 is clothed with elegant hairs of various forms, but very regularly 

 arranged, while the internal surface of the pouch exhibiu peculiar 

 hairs, consisting of two cells, each running out into a longer or 

 shorter arm. 



In leaves, aa in plants in general, all forms are possible, and almost 

 all actually existing strict stereometric forms exceptod. The termi- 

 nology depends either on comparison with mathematical figure*, or 

 with objects presupposed to be familiar in common life. There U no 

 scientific rule for this ; testhetic tact alone must be our guide. But 

 within the HmiU of certain vegetable groups certain circled of forms 

 do exclusively occur ; and under the guidance of accurate observation 

 we can here establish more definite mode* of nomenclature, which 

 however are only valid for these definite groups. 



If the Cotyledon of most Monocotyledons is examined we find that 

 in iU gradual development it completely incloses the Terminal Bud 

 ( Pluinulu) ; indeed that the exceedingly delicate soft cells of the two 

 borders of it become in part so firmly united that they may be 

 regarded as grown together, only a little fissure, which exUU in all 

 Monocotyledons, remaining. In germination the developing bud has 

 not room to protrude through the little fissure, so that it pushes the 

 borders of it more or less forward, and then these appear aa a peculiar 

 appendage on the middle of the Cotyledon, as a membranous expan- 

 sion of the border of the lower port of the leaf, or as lubes on iU 

 base. Similar conditions also occur frequently in the later leaves. In 

 the Dicotyledons a like condition present) itself not uufrequently; 

 either the borders become expanded like a membrane on the base of 

 a petiole or stalk-like leaf, or the emerging bud lifts up a longer or 

 shorter membranous sheath, or peculiar lobules are formed on the 

 base of the petiole, sometimes assuming the form of leaflets, and even 

 connected with the petiole by an articulation. In all cases, without 

 exception, they are, from the course of the development, parts of a 

 leaf developed principally at iU base, and in their essential nature 

 wholly identical structures throughout all the Phaneroyamia, though 

 they may vary most abundantly in their appearance. They have 

 acquired very different names. In the Qraaaea these parts ore called 

 the Ligule (Ligula) : in other Monocotyledons, sometimes Vagina 

 Stipularis, if large and rising free from the lowest part of the leaf; 

 Vagina Petiolaru, if smalt and showing itself first higher up the leaf: 

 in the Dicotyledons, ' Petiolus Alatus, StipuUc Aduatv,' if on the 

 margins of the leaf-stalk ; Ochrea, if sheathing, as in the Polyyonacete; 

 or Stipules (Stipule), if appearing like special leaflets stationed beside 

 the base of the petiole : lastly, in the floral leaves, Foruix, Corona, 

 Nectarium, *c., aa iu 7/ycAnu, llorayinacar, A'arciuut, Ac. They 

 occur as stipules, especially in compound leaves, where sometimes 

 they alone are developed into a flat surface, while the leaf itself 

 merely forms a filiform process for example, in Latkyrui Aphaca. 

 At the base of the leafleU of compound leaves also-little lobes some- 

 time* occur, which, perhaps originating in the same manner, are called 

 Stipelles (Stipelle). 



Every leaf, as already observed, originates as a little conical papilla 

 at a definite point on the circumference of the axis. Even the 

 sheathing leaves are produced in this manner, and at the point which 

 corresponds to the middle line (the mid-rib) of the future leaf by 

 degree*, and as it is pushed up further from the axis the part* of its 

 circumference take part more and more in the development, and thus 

 the base of the leaf gradually become* broader, until it completely 

 surrounds the axis. If the development of cells, or the expansion 

 of existing ones, continue* on the borders of the base of the leaf 

 beyond the degree required to surround the axis, the newly-formed, 

 still soft, and almost gelatinous cells of the two borders of the base 

 of the leaf become applied to one another, anil become united as 

 firmly a* the cells of a continuous tissue ; iu this way the lower part 

 of a leaf then becomes a closed undivided whole surrounding the axis. 

 If the lateral production of cells is small, and the union takes place 

 relatively early, this closed portion forms a longer or shorter sheath, 

 closely embracing the axis (vagina olausa), as in many Grasses. If, on 

 the contrary, the lateral cell-production or expansion U considerable, 

 and occurs relatively late, so that merely the base of the leaf forms a 

 flat projecting border round the axis, the leaf is said to have the stem 

 growing through it (folium perfoliatum) Bupleurum perfoliatum, for 

 example. When the axis is angular, and produces thin more or leas 

 projecting plates upon these angles (the so-called winged axis, ' axis 

 alatu*'), a similar process may enter iutu the bud iu such a way that 



