GROWTH AND DEVELOPMENT OF THE INFLORESCENCE AND FLOWER 505 



inner bracts form small laminas. This result is not unlike that obtained 

 in some experimental studies of heteroblastic phenomena in vegetative 

 shoots ( Figure 12 ) . 



Although the time, or season, of the beginning of inflorescence has 

 been the subject of some published investigations, chiefly relating to 

 economic plants such as fruit trees, not enough is known of this impor- 

 tant aspect of the biology of flowering plants; but reference can be 

 made to the work of Grainger (1939). Very considerable variation in the 

 time of inception and development of the inflorescence in diJBFerent 

 species is found: in some perennial species, the floral development is 

 well advanced by autumn; in others it does not take place until the fol- 

 lowing spring or early summer. The relationships between these devel- 

 opments and factors such as day-length, temperature, etc., requiie 

 further investigation, while the search for favorable materials for 

 observation and experiment is itself an engaging task. It is also worth 

 noting that the time of inception of the inflorescence in relation to the 

 development of the plant may sometimes have important practical 

 aspects— e.g., in the application of fertilizers and other cultural treat- 

 ments ( Wardlaw, 1959, 1960 ) . 



Carr and Carr (1959) have noted some interesting points about 

 the complex inflorescences in species of Eucalyptus. For example, some 

 of the characteristic features of the inflorescence pattern are reflections 

 of morphological features peculiar to the shoot system : the outer bracts 

 resemble the adult leaves in their asymmetry about the midrib. Leaf 

 and bract primordia originate decussately at the shoot apex, but in 

 most species the leaves of each pair become separated by the develop- 

 ment of a segment of axis (an "intranode") between them. In certain 

 species this development leads to the splitting apart, or "disarticula- 

 tion," of the unit inflorescence into two subclusters. Some very complex 

 inflorescences thus result from the disarticulation of a simple inflores- 

 cence, followed by other developments. The authors conclude that in- 

 florescences with few flowers and with free, persistent bracts, the 

 number of which is related to the flower number in the cluster, are 

 phylogenetically primitive, whereas inflorescences with many flowers 

 and fused bracts, constituting a caducous involucre in which the num- 

 ber of bracts is not related to the number of flowers, are advanced. 

 Though causal in its inception, this investigation has thus enabled im- 

 portant phylogenetic conclusions to be drawn. 



The manner of flower formation in species of Nymphaeaceae bears 

 out some of the basic points advanced in this paper (Cutter, 1957- 

 1960). In Nuphar and Nymphaea spp., as we have seen, flower pri- 

 mordia originate as circular mounds on the surface of the rhizome 

 apical meristem in positions on the genetic spiral which are normalK' 

 occupied by leaf primordia. The destiny of growth centers must there- 



