Brown: Regeneration in Phegopteris t'olypodioides 395 



their growth was very rapid. They resembled, in all respects, the 

 leaves of a normal young sporophyte of this species of fern (Fig. 

 3) ; although the blade of the second leaf was somewhat simpler 

 in form, having only two main divisions, each of which was lobed, 

 instead of three main lobed divisions. However, such irregulari- 

 ties are to be noted in leaves of normal young sporophytes of this 

 and other species of ferns. These two leaves attained a height of 

 6 mm. The third leaf, which was much slower in growth and 

 development reached a height of only 4 mm. and was much 

 simpler in form. The blade consisted of only two lobes, which 

 were entire. The fourth leaf showed still greater simplicity in 

 form and reached a height of only 3 mm. The blade was 

 almost entire, with a slight lobe on the one side. The blades of 

 these latter leaves, like those of the first and second ones, bore 

 stomata. 



Discussion and conclusion 



The various theories which account for regeneration, as ad- 

 vanced by the many writers on the subject, consider the following 

 influences: (i) external influences to which the plant is subjected; 

 (2) tendencies inherent in the plant body. 



The factors considered as the possible controlling or influencing 

 ones may be placed in the following classes: (i) nutrition dis- 

 turbances; (2) wound stimuli; (3) changes in the water content; 

 (4) the accumulation, at certain places, of definite formation 

 substances; (5) the presence of dormant or latent rudiments; 

 (6) correlation; (7) age and maturity of the parts; (8) form 

 disturbance; (9) growth tension; (10) interruption of the func- 

 tions of respiration, transpiration or photosynthesis; (11) iso- 

 lation from the influence of the whole; (12) presence of enzymes 

 which are responsible for the formation of the part regenerated. 



The fact that regeneration was never observed in attached 

 leaves of Phegopteris polypodioides and did occur in a leaf which 

 had been separated from the plant would seem to indicate that the 

 separation from the repressing influence of the plant body played 

 an important part, as beheved by Loeb (4, p. 153); although the 

 fact that cases have occurred in other species of ferns when the 

 leaves were still attached would not seem to refute this theory. 

 Experimental evidence has shown that many species of ferns, 



