CLASSIFICATION OF THE PRIMORDIA 89 



etc.). All these individuals,^ whatever may be their nature, 

 have a definite position. Each of them may he regarded, as a 

 imiaxial system in which several primordia may be discerned. 

 Moreover, the leaves, petals, stamens, etc., may be ramified in 

 their turn (leaves of TrifoUum, petals of Reseda, stamens of 

 Fumaria, etc.). In all the segments produced in this way 

 primordia may be discerned according to the scheme in § 72. 

 Similar principles axe appUcable on the trichomes (hairs, glands, 

 etc.). (See §§ 57, 60.) 



Certain primordia are not mentioned in § 72. Some of them 

 are important, for instance : 



(i) Certain segments (individuals) may be united. In a 

 gamopetalous corolla (or gamosepalous calyx) the parts are 

 united into a cup, tube or ring. The stipules are detached 

 from the leaf or adhering to the leafstalk or imited into a ring 

 or sheath round the stem, etc. 



All such properties - axe mentioned or described in the floras : they are 

 almost always easily measurable. Examples : In a gamophyllous corolla 

 or calyx we may measure the length of the tube, the length and the breadth 

 of the free portions (segments, lobes, teeth). In a leaf of a rose, we may 

 measure the total length of the stipules and the length of their free portion. 



(2) The colours : each colotir is measurable by means of a 

 scale of colours or by a chemical or spectroscopical analysis. 



§ 74.— RAMIFICATION OF THE UNIAXIAL SYSTEM. 

 COMPLICATED CASES [conUnued) .—Th.e different sorts of 

 units (cauloms, phylloms and trichoms) which constitute a 

 ramified system, their relative position and the forms of rami- 

 fication are described in the classic literature on morphology 

 and phyllotaxis (including the floral diagrams). 



Let us now compare two specimens, a and b, with regard to 

 a given property ; for instance, the length of the leaves. This 

 property is almost always very variable within the limits of each 

 specimen ; the differences depend for a part on social causes 

 (place of the leaves).^ For a comparison between a and b the 

 social differences ought to be eUminated. When a leaf a has 

 been measured in « we want to find and to measure in 6 a leaf /8 



'The difierences between the individuals alluded to are comparable to the 

 difierences between different sorts of specialized individuals observed in certain 

 polypoid animals. 



' Whatever may be their morphological significance. 



' All the leaves of a specimen (for instance, a tree) are individuals of a certain 

 sort which belong to one society (just as certain specialized individuals in 

 certain polypoid animals). The variation of each of their primordia (for 

 instance, their length) is in part a consequence of plasticity (external causes); 

 for another very important part a consequence of social causes (gradation. 

 Part VIII.). 



