DIMORPHISM OF FERNS. 



343 



leaves, the general plan of which is the same, and we recognize 

 each as being a leaf. 



626. Transformation of the fertile leaves of onoclea to 

 sterile ones. It is not a very rare thing to find plants of the 

 sensitive fern which show intermediate conditions of the sterile 

 and the fertile leaf. A number of years ago it was thought by 

 some that this represented a different species, but now it is known 



Fig. 447. 

 Sensitive fern, showing one vegetative leaf and two sporophylls completely transformed. 



that these intermediate forms are partly transformed fertile leaves. 

 It is a very easy matter in the case of the sensitive fern to pro- 

 duce these transformations by experiment. If one in the spring, 

 when the sterile leaves attain a height of 12 to 16 cm (8-10 

 inches), cuts them away, and again when they have a second 

 time reached the same height, some of the fruiting leaves which 

 develop later will be transformed. A few years ago I cut off the 



