CONTACT-PRESSTTRES. 245 



Perennating rhizomes taken from January to March show, within the coiled 

 leaves of the current year, the primordia of the next season just com- 

 mencing. On removing the chaffy scales, these appear as papillae, some 

 quite visible to the naked eye, and also quite isolated from one another : 

 Hofmeister's empirical generalisation, that each new member falls 

 asymmetrically in the widest gap between two older ones, is as patent 

 as in any small bud that requires to be sectioned. The system is made 

 clearer by removing the entire apex, about ^ mm. thick, and rendering 

 it transparent in Eau de JaveUe (fig. 35). 



Although destitute of lateral contact-pressures, the primordia 

 arise each in normal position for (3 + 5) or (5 + 8) systems, and the 

 lines drawn through empirical centres of construction form spirals, 

 which intersect in the central region very approximately at right 

 angles, so far as can be judged by the eye : the fact that this is the 

 true structural condition being checked by examination of the 

 stellar meshwork in the adult part of the shoot. 



Again, consideration of the cell-structure of the apex of Aspidium 

 root (fig. 18) shows clearly the general law of pressure as affecting 

 younger members. Any younger cell can always grow successfully 

 against all the pressures of older ones of the same character, and 

 the apical cell grows against the pressure of the entire mass, and 

 retains its walls always convex outwards. Similarly, any younger 

 member can always compress an older one, and is therefore not 

 essentially affected by it. In transverse sections of free leaf- 

 producing buds, the primordia are again always convex outwards, 

 and the preceding members become flattened: an example is 

 afforded by Araucaria (fig. 41); new lateral buds flatten their 

 subtending leaves, which would otherwise have remained rhom- 

 boidal in section. In more typical plants the older leaves them- 

 selves tend to assume a flattened appearance owing to their 

 progressive bilaterality, so that the effect seen may not be due to 

 one cause alone. In fact, when it is borne in mind that in a 

 typical foliage-bud the axis which includes the leaf-insertions is 

 growing and expanding simultaneously with the young primordia 

 arising from it, it is clear that the subject of hud-pressures requires 

 very careful handling, since when the whole system is growing 

 uniformly there may be absolutely no pressures in the bud at all, 

 the conventional expression " packing in the bud " being largely 



