i66 



EXTERNAL CONFORMATION OF PLANTS. 



of the leaves then makes it sufficiently clear which is mother-shoot and which lateral- 

 shoot in the sympodial pseud-axes. Sometimes, however, distortions occur {e.g. in 

 Solanaceae) which might lead to erroneous conclusions if reference was not made to the 

 earliest conditions of development. 



Sect. 26. The Relative Positions of Lateral Members on a Common 

 Axis\ — In order to bring the facts which we have now to consider into a clear 

 and simple arrangement, it is necessary, in the first place, to explain the use of a 

 few technical expressions and geometrical modes of representation. 



By the term Axial Structure or Axis is to be understood, in future, when the 

 contrary is not expressly stated, every member that continues to grow at its apex 

 and produces lateral members ; for example, a mother-root with its lateral roots, 

 a stem with its leaves, the mid-rib of a leaf with its leaflets laciniae or lobes, or a 

 thallus-shoot with its lateral outgrowths. 



If two or more similar lateral members proceed from one transverse zone of 

 an axis in different directions, they compose a Whorl. A true whorl results when the 



zone of the axis which produces it 

 is transverse from its origin (Fig. 

 136); a spurious or pseudo-whorl 

 arises when the zone is the result 

 of unequal development of the axis, 

 or when lateral members which were 

 formed side by side have become so 

 far separated by subsequent unequal 

 elongation of the axis, that they ap- 

 pear, in the mature state, distributed 

 into different zones. Simultaneous 

 Whorls are those whose members or 

 rays are formed simultaneously (Fig. 

 136). Successive Whorls are formed 

 when the members at a zone grow 

 in succession either advancing right 

 and left from one point of the peri- 

 phery, as is shown in Fig. 137, and 

 as occurs in the true leaf-whorls of 

 Chara ; or when the development 

 takes place in a different order, as in 



F,G. x37.-Development of the flower of the mignonette (after Payer, ; the trUC Icaf-whoris Of Salvinia {vidc 



to the left a younger, to the right an older bud ; from the latter the ante- ^,,fvr,\ onrl in tl->c» tVir/^^ r\r- 9i\ia 



riorsepals J have been removed, the posterior ones left; //petals ; j; W^^)y ^^^^ '" ^"^ LUrCC- Of TIVC- 



stamens, the posterior ones already large, the front ones not yet even in ,^ortArl <^o1\;^ac r»f tnnct PVranArrKTQmc 



a rudimentary state ; c the carpel or rudiment of the fruit. partCQ Caiy CCS 01 mOSl r naUCrOgamS. 



Fig. 136. — Apical region of a shoot of Coriarta viyrtifolia ; at .^ in 

 transverse section, S in longitudinal section ; s apex of the stem ; d b leaves 



in pairs, i. e. in decussate whorls of twos ; k axillary bud ; g yot 

 vessel. 



igest 



^ Roper, Linnoea, p. 84. 1827. — Schimper-Braun, Flora, pp. 145, 737, 748. 1835. — Biavais, 

 Ann. des Sci. Nat., vol. VII. pp. 42, 193. 1837. — Wichura, Flora, p. 161. 1844. — Sendtner, Flora, 

 pp. 201, 217. 1847. — Brongniart, Flora, p. 25. 1849 — Braun, Jahrb. fiir wissen. Bot. I. p. 307. 1858. 

 — Irmisch, Flora, pp. 81, 497. 1851. — Hanstein, Flora, p. 407. 1857. — Schimper, ditto, p. 680. — 



Buchenau, Flora, p. 448. i860. — Stenzel, Flora, p. 45. 



[86 = 



-Numerous papers by Wydler, e. g. 



Linngea, p. 153, 1843 ; Flora, 1844, 1850, 1851, 1857, 1N59, 1S60, 1863 ; and elsewhere. — Hofmeister, 

 Allgemeine Morphologie der Gewebe, §§ 8, 9. Leipzig 1868. [Haughton, Manual of Geology. — 



