CONTACT-PRESSURES. 259 



amount of mutual pressure is determined solely by the relative 

 rate of growth of the receptacle and the fruits ; and if the growth 

 of the former be only sufficiently active, contact-pressures would 

 be entirely eliminated.* 



Fig. 90. — Euphorbia Wulfenii, Hoppe, Terminal system of a strong shoot (8 + 13), 

 showing progressive dorsiventral bilaterality o£ the members. 



* A good example is afforded by the growth of the capitulum receptacle 

 in Budbeckia and Scabiosa: e,.g. in Scabiosa atropurpurea the florets form a 

 gradated series, but the fruits are required to be all the same size. The axis 



