^4 



(" Linn. Soc. Journ." \'ol. XXXV, Xo. 248\ Such an arrangement produces a 

 flat, exposed, transpiratory surface, as distinct from the concave, cr3'ptic surfaces 

 usually obtaininsj in the concrescent leaves of the whole genus. 



growmg 



Cal/itris trees, however, 

 under the usual 

 climatic conditions prevailing 

 in Australia, have leaves 

 characterised by a marked 

 concrescence or decurrence 

 on a centra] stem, and each 

 leaf separated by a narrow 

 passage formed by the ventral 

 surfaces, the edges of which 

 appear to have the power of 

 opening and closing the chan- 

 nel thus formed, and exposing 

 the stomata to light and air, 

 or shielding them according 

 to the exigencies of favourable 

 or adverse climatic changes. 



Several theories have been 

 advanced to explain the 

 reason for this decurrence 

 in plants, more especially in 

 Conifers, and according to 

 [Masters ("Journ. Linn. Soc." 

 Vol. XXVII, Bot. No. 183- 

 184J Mechan "considers tliat 

 this adnation is specially 

 characteristic of vigour, while 

 the free leaves indicate a 

 state of weakness and arrested 

 growth " ; and Masters agrees 

 witli this view and then 

 states, " But if the distinction 

 between growth and develop- 

 ment be kept in mind, it 

 would seem that the concrescence is an indication of arrested and irregular 

 development associated with disproportionate rapidity of growth. In tlie free 

 leaves the balance between growth and development is preserved, the base of 

 the leaf is symmetrical and the parts arc all in n j^ular proportion." 



Flgaf« 1, — Onr-ycAT fAd Callttrii, ^howinK how early in the plant's 

 lifp \y the transition from free leaves to decurrent ones. 



N.lt. MZ. 



