MULTIJUGATE TYPES. 



187 



system is often very marked. (Dianthus, Phlomis (fig. 73), 

 Urtica, etc.) 



These irregularities in petiole formation, etc., might evidently 

 occur to an equal extent in asymmetrical systems, but they would 



Fig. 71. — Epiloliv/m a/ngustifolium, L. — I. , section some distance above the apex of a 

 perennating shoot. II., section exactly at the apex, symmetiioal (2 + 2) system. 



not be so readily noticed, owing to the difficulty of judging the 

 error of such constructions by the eye alone.* 



* If two equal and similar leaf-primordia meet around an axis and tend to 

 pack, the chances are that, if the ends are ■well developed and rounded, one will 

 slip under the other on one side and over the other on the opposite side. The 

 two developing members thus become pushed askew with regard to their true 

 position and that of adjacent members, and an irregular effect is produced. To 

 test true symmetry (2 + 2) as opposed to bijugate (2 + 4) construction, it is 

 necessary to cut the primordia at the apex before they commence to overlap 

 (fig. 71, 2). Again, such secondary confusion will be greater in a symmetrical 

 construction where the primordia of the same whorl should exactly meet, since 

 in the case of asymmetry the paths for slipping are provided in the spiral con- 

 struction. Hence a symmetrical system tends to give greater secondary irregu- 

 larity than an asymmetrical one, and it is thus rather the exception than the rule 

 fo: a decussate plant to show four strict orthostichies. The externally visible 



