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 



