THE BILATERALITY OF APPENDAGES. 299 



appearance has been noted by Sachs as a secondary phenomenon 

 presenting no real objection to the primary construction of tissue 

 masses by orthogonal trajectory curves {cf. Sachs, Physiology, 

 p. 433). Thus a slight displacement in a primary orthogonal (5 + 8) 

 system has little effect in altering the construction as a whole, 

 and the diagram closely represents the fact observed in a section 

 of the adult stem-apex of Nymphaea (fig. 110). 



Secondly, the existence of similar slipping in the form of a growth 

 adjustment has already been shown to occur in connection with 

 the arrangement of lateral axes which have only a subsidiary 

 connection with the primary system of foliar appendages. Thus, 

 in the stock examples of the Eeliardhus capitulum, ihe Pine-cone, 

 and the Aroid spadix, it was evident that any secondary ex- 

 tension of a member which was not a foliar appendage, either 

 radially or tangentially, must produce a similar sliding effect ; the 

 " stepping '' affecting different curves according to the geometrical 

 necessities of the construction. That is to say, any variation in 

 the bulk of a lateral appendage at a point beyond its insertion will 

 produce alterations in the system if section takes the members at 

 this point ; and it must be remembered that the transverse section 

 of a typical bud with dome-shaped apex cuts the peripheral 

 members at a higher level of their course than in the case of the 

 youngest primordia. Further, a tendency of a leaf-primordium to 

 become wider tangentially in some part of its course, above its 

 insertion, may also be taken as typical for the great majority of 

 foliage-buds. Any such increased tangential growth of a prim- 

 ordium at a point above its base, while these insertion-areas still 

 constitute the surface of the axis, must necessarily involve a 

 readjustment slipping of the same type as that found in the scales 

 of the Pine-cone ; that is to say, the short curves will become 

 stepped. Variations in the bulk of the appendage at different 

 parts of its length will thus produce sliding effects in both 

 asymmetrical and symmetrical systems : in the former the sliding 

 wUl follow the tangential diagonals in an orderly manner, since 

 the paths of such sliding are left obvious in the construction ; but 

 in the case of symmetry the overlapping will be quite irregular, 

 since normally the primordia should accurately meet at their 



