BROWN: REGENERATION IN PHEGOPTERIS POLYPODIOIDES 395 
their growth was very rapid. They resembled, in all respects, the 
leaves of a normal young sporophyte of this species of fern (Fic. 
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: (1) 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: (1) 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 believed 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, 
