62 PRINCIPLES OP PLANT-TEEATOLOGT. 



the number of members is apparently taking place from 

 within outwards, as is natural, seeing that the apex 

 was the primitive growing point of the shoot. The 

 inauguration of the spiral arrangement is seen in the 

 passage of a member of one whorl to the whorl next 

 outside it; we see, for example, a member of the outer 

 perianth (calyx) becoming transformed into a bract 

 and displaced downwards, owing to the development 

 of an internode ; the gap so caused is filled by a 

 member of the inner perianth- whorl (corolla), which 

 in its turn is supplied from the androecium. This may 

 be regarded as an instance of reversion (more or less 

 imperfect) to a kind of spiral phyllotaxis. It causes a 

 twisting of the peduncle of the flower. The change to 

 the spiral arrangement is probably the primary factor 

 in these flowers, and the formation of a bract from a 

 sepal is a secondary phenomenon resulting therefrom. 

 Other instances will now be given of abnormal 

 increase in the different whorls taken from various 

 plants ; in these cases the other whorls are, as a rule', 

 unaffected. 



(1) Calyx. 



In the lesser celandine {Ranunculus Ficaria) the 

 normal number of sepals is three ; Celakovsky figures 

 flowers with 4- and 5-merous calyx ; as calyx and 

 corolla are intimately united into one genetic spiral, 

 the number of sepals will determine the position of the 

 following petals. It is very frequent in many plants 

 for an extra sepal to occur while no other part of the 

 flower is modified. 



A drawing of a flower of Cypripedium insigne showed 

 the usually single posterior* sepal behind the lip 

 divided into two, one on either side of the lip (PI. 

 XXXV) ; there is also a drawing by Mr. Hansen in 

 the British Museum which shows the same thing in 



* In all descriptions of Orchid-flowers the primitive condition of the 

 flower is referred to before the ovary became twisted, except in those oases 

 where these terms are between inverted commas. 



