CHAPTER IV. 



THE PRINCIPLE OF ARRANGEMENT. 



m. ISM n.z2.m9 i(j.si 



Superposition and xAlternation of Whorls. — It has been 

 already observed that leaves are ai-ranged on two methods, 

 either being on the same plane, i.e. opposite and verticillate ; 

 or with only one at a node, i.e. alternate. If the fibro-vascular 

 cords passing from the leaves into 

 the stem be traced downwards, 

 those belonging to the leaves ^S 

 situate in one and the same ver- 

 tical line always have their lower 

 extremities inserted laterally and 

 not actually confluent in that line, 

 as will be seen in Fig. 7, taken 

 from Hanstein's researches.* 



This fact is trne, not only for 

 foliage and bracts, but also to 

 some extent for sepals and petals. 

 When, however, we trace the 

 origin of stamens and carpels, we 

 find that their cords, instead of 

 being inserted separately into the fibro-vascnlar cylinder, 

 generally arise by branching, or by the so-called " chorisis " 



* De la Connexion qui existe entre la Disposition des Feuilles et la 

 Structure de la Zone Ligneuse des Dicotyledons, Aun. des. Sci. Nat., 4® 

 Ber., torn. 8. 



2.7. 4. dJ e. 3.8. S. 



Diag^-am of the foliar cord^ in 

 the stem of the Arabis albida (after 

 Hanstein). 



Fig. 1 



