64 PRINCIPLES OP PLANT-TBEATOLOGT. 



two very interesting and very rare abnormal flowers 

 of Nymplisea : in one of these the median posterior 

 sepal 3^ of the normal flower was replaced by a two- 

 fold sepal, in the other by two distinct sepals occupy- 

 ing precisely the position of sepals 3 and 5 in Nuphar 

 (fig. 83 a) ; hence this represents without doubt the 

 original structure of the calyx in Nymphsea. But this 

 position of sepals 3 and 5 necessarily involves the 

 former presence of a sepal (4) in the same (median 

 anterior) position in which we find it in Niiphar. 

 During the process of reduction from 5-mery to 

 4-mery in the calyx this median anterior sepal has 

 disappeared owing to the transposition of the bract 

 into that -position. This reductive change has induced 

 a similar change in the first two whorls of the corolla. 



In Veronica frequently the odd posterior sepal, 

 which has been eliminated owing to fusion of the two 

 lateral posterior petals to form the single large median 

 one (which would then come to lie opposite the median 

 sepal, thus interfering with the law of alternation), 

 becomes added to the diagonally-placed calyx. But 

 there is a section of the genus named by-De Candolle 

 Pentasepal^, in which a small fifth posterior sepal is 

 normally present. Camus found a fifth posterior sepal 

 occasionally present in V. serpyllifolia ; but it also 

 occurred sometimes in the anterior position, and opposite 

 the small anterior petal, thus showing that its presence 

 there was not due to torsion of the flower. It seems 

 that Noll also observed in two flowers of V. longifolia 

 an anterior fifth stamen ; while Schlechtendal, in the 

 same species, observed a 6-merous calyx having both 

 a posterior and anterior median sepal. In all these 

 cases the anterior sepal is probably due to bipartition 

 of one of the lateral anterior sepals. 



In most grasses, owing to the tendency of their 

 flowers towards a 2-merous construction, whereby the 

 two posterior sepals become fused to form a median 

 posterior sepal and the two lodicules tend similarly to 

 unite to form an anterior median petal, the anterior 



