GLANDS 



47 



Retrograde Metamorphosis. — In all of these cases the change is from 

 a more complex organ, or one of higher rank, to one of a lower, and is 

 called Retrograde Metamorphosis, or Reversion of Type. 



Progressive Metamorphosis also occurs. It is seen in the gradual 

 transformation of bracts, themselves transformed leaves, into sepals 

 in the Barberry (Fig. 61), and of sepals into petals and petals into 

 stamens. Even stamens may become metamorphosed into carpels 

 or carpels into stamens, one instance being the flowers of the willow, 

 where organs have been seen intermediate in appearance between the 

 two. 



62. 



Fig. 61. Structures from flower of Berberis, intermediate between petal and stamen. 62. Same 



from flower of Castalia. 



Teratology. — Cases of abnormal retrograde metamorphosis are very 

 common, and have given rise to a separate department of study known as 

 Teratology. 



Enation or Outgrowth. — Enation and the effects produced by if are well 

 illustrated in one of their forms by the petals of certain genera of the 

 Ranuneulaceae. The retention of a drop of nectar at the base of the 

 petal of some species of buttercup is effected by the presence there of a 

 minute scale (Fig. 63), covering over a slight depression. The nectar 

 is partly lodged in this pit, partly held between the petal and the 

 scale. In the Coptis (Fig. 64), a closely related plant, the depression 

 is deepened into a more obvious cavity and the scale is dispensed with, 

 while in the Delphinium (Fig. 65) the cavity becomes a long tube. 



Glands. — Although the detailed consideration of appendages will 

 be taken up in connection with the several organs to which they apper- 



