CONTACT-PRESS QRES. 251 



and at first sight the (5 + 8) system has been quite destroyed ; but 

 coiriparison of lines drawn through the central bundles of the leaves 

 shows that it may still be traced with sufficient accuracy to admit of 

 numbering the members. 



The Gedrus bud thus represents a case of simple radial com- 

 pression of the older leaves of a (5 -f- 8) system against a circular 

 boundary, the result being merely to produce irregular and often 

 hexagonal figures; that is to say, owing to the effect of radial 

 pressure the plastic masses of the older leaves are squeezed into 

 irregular shapes, but they do not roll over one another to any 

 extent. The phenomenon is rather one of adjustment of growth 

 than of actual displacement, the centres of construction indi- 

 cated by the vascular bundles remaining very fairly in their 

 places. In dealing with such packing of leaf-primordia no 

 analogy can be drawn corresponding to that of the packing of 

 spheres into the hexagonal arrangement of the " pile of shot." 

 The action of a radial compressing force, here provided by the 

 overarching of the crater wall on the developing system, does not 

 tend to produce displacements in any way comparable to those 

 of the original Dachstuhl theory ; the only result of such 

 additional radial compression being the production of irregular 

 figures resembling those seen on cutting a piece of ordinary 

 parenchymatous tissue: the system tends to become irregular, 

 but it is quite clear that no radial (i.e. vertical) compressing 

 force acting on such a circular asymmetrical system would ever 

 so change it that the system would after displacement retain 

 a regular construction. The fact that in the general case 

 phyllotaxis systems normally retain regular parastichy curves is 

 therefore the proof that no extra pressures beyond those of the 

 growing primordia are normally in operation. 



Similarly, pressure against the relatively greatly developed 

 cotyledons to a certain extent affects the shape of the first small 

 needle-leaves of the seedlings of Conifers (Pinus, Gedrus). That 

 such seedlings possess, so far as can be seen, an irregular phyllo- 

 taxis system may be due to more than one cause : that the 

 actual curve constructions are at first anomalous and even some- 

 times symmetrical may be traced from sections which show the 



