CONTACT-PRESSURES. 257 



to fit into a square mesh of the phyllotaxis system together with 

 the crushed subtending bract. The result is that the ovals with 

 their long axis in the " median plane " of the flower are so adjusted 

 that they come to lie obliquely across the quasi-squares, but with- 

 out otherwise interfering with the curve construction. The radial 

 extension of the ovaries, that is to say, breaks the long curves, 

 giving them a serrated or step'ped appearance, but the short curves 

 remain unaffected. 



This implies, however, no displacement whatever of the orthogonal 

 construction system : the centres of construction remain unaffected, 

 there is a change of shape, but not of position, so that the pheno- 

 menon is again not one of displacement but rather of readjustment. 



Section of a young capitulum, for example (fig. 89), at the level 

 of the style canals, gives a series of points which can be taken 

 accurately for each flower ; the curves drawn empirically through 

 these points show the theoretical square meshwork with as great 

 a degree of accuracy as could be expected from a plant. The dis- 

 placement of the florets is thus apparent and not real, and the 

 effect of any radial elongation of members arranged in a spiral 

 phyllotaxis series will be to step the long cMrves, while the short 

 curves remain unaffected. 



That some alteration in the phenomena of the curve-systems 

 should therefore be observed in Eelianthus in passing from the 

 flowering condition with florets circular in section to the fruiting 

 condition with radially elongated achenes, is sufficiently obvious.* 

 But such alterations have no reference whatever to the causes 

 which produced the primary system of subtending bracts ; nor 

 does such a phenomenon enter into the question of the primary 

 importance of contact-pressures. The bicarpellary ovaries do not 

 assume the flattened form in consequence of mutual pressure ; 

 their flattened form is as much an inherent growth function as 

 that of the two-carpelled fruits of the Umbelliferae : it is easy to 

 see by cutting a capitulum in two, or by noting the shape of fruits 

 adjacent to ovaries which have proved sterile, that the flattening 

 of the fruit is quite independent of any pressures, although mutual 

 pressures may make the angles more pronounced. The changes 

 * Bot. Zeit., 1902, pp. 226, 230. 



