6 Development of the Fern Leaf 



leaves and the mature leaves in consequence appear sooner than 

 if the plant is weak: the first leaf, also, produced by the plant 

 often portrays a more advanced stage of development and the 

 height of leaf-development attained is sometimes greater. The 

 leaves of a sickly plant often portray minute gradations of change. 



There is evidence which tends to show that if a plant's vitality 

 be suddenly lowered, as, for example, by an injury, the first leaf 

 the plant produces afterward may portray a lower stage of de- 

 velopment than the last leaf it produced before, and it may or 

 may not produce additional leaves before the height of leaf- 

 development previously attained in its series of leaves is again at- 

 tained. But more evidence is needed on this point. The most 

 striking apparent case of the kind that I have seen is the follow- 

 ing: 



The series of leaves produced by a young plant of Asplenium 

 ebenoides had passed the stage of leaf-development at which, in 

 this species, the leaf is simple, and had reached the stage at which 

 the leaf is deeply pinnatifid, when the flower-pot containing the 

 plant was broken and only a little earth left on the roots. The 

 plant was allowed to remain in this condition for some days 

 before it was re-potted, and some of its leaves were cut off. It 

 then produced simple leaves again, and then a series of leaves 

 leading again to the pinnatifid stage. But as A. ebenoides is a 

 hybrid, and as one of the parent species has simple leaves, the 

 case can be called merely one of temporary partial reversion to 

 a parent type. 



It is evident that conditions of environment can lessen or 

 increase a plant's vigor, and so indirectly lessen or increase the 

 degrees of development shown by its leaves individually. Little 



