i88 



MORPHOLOGY OF MEMBERS. 



Chara ; or in a different order, as in the true leaf-whorls of Salvinia {vide infra), 

 and in the three- or five-parted calyces of most Phanerogams. 



The lateral members are, on the other hand, isolated or scattered when each 

 member stands on a different zone of the axis. If the surface of an axial structure 

 (which sometimes is quite imaginary, as in Nephrodium Fitix-mas, &c.) is supposed 

 to be continued through the base of each lateral member, the section forms its Plane 

 of Insertion. An imaginary point in this is considered its organic centre, but does 

 not usually correspond to its geometrical centre ; this point may be termed the Point 

 0/ Insertion (see Sect. 27). A plane which bisects a lateral member symmetrically, 

 or divides it into two similar halves, and contains the axis of growth of the lateral 

 member as well as that of the axial member, passes through the point of insertion, 

 and is called the Median Plane of the lateral member in question. If members are 

 so arranged at different heights on an axis that their median planes coincide, they 

 form a straight row or Orthostichy ; generally there are two, three, or more orthostichies 

 on an axial structure, and the members are then said to be recti-serial. If there are 



Fig. 146.— Diagrams of a shoot with the leaves arranged 

 with a uniform divergence of ^. 



Fig. 147. — Diagram of the flower-stalk of Paris quadri- 

 folia; //whorl of the large foliage-leaves beneath the flower; 

 ap outer, ip inner perianth-whorl ; aa outer, ia inner stamens ; 

 in the centre is the rudiment of the pistil consisting of four 

 carpellary leaves. 



no orthostichies, /. e. if the median planes of all the members intersect one another 

 on an axis without coinciding, their arrangement is solitary. 



The angle which the median planes of two members of the same axis 

 enclose is their Divergence ; it is expressed either in degrees or as a fraction of 

 the circumference of the axis, which is then supposed to be a circle, although in 

 fact this is not usually the case. In Order to represent the divergences clearly, they 

 may be drawn on a horizontal section of the vertical axial structure, in the manner 

 represented in Figs. 146 and 147. The transverse sections of the axial structure 

 which bear the lateral members — in this case leaves — are denoted by concentric 

 circles, the outermost circle corresponding to the lowest, the innermost to the 

 highest transverse section. On these circles, which thus represent the relative 

 ages from without inwards according to their succession in the acropetal develop- 

 ment of the axis, the positions of the members are denoted by dots, or the forms 

 of the planes of insertion themselves may be approximately indicated, as in the 

 figures. On such a projection or diagram the median planes of the members 



