158 
THE FERN FAMILIES OF BRITAIN. 
the head, the result being that the arrested sporangium 
ultimately appears as a club-shaped body of larger size than 
the normal sporangium. The individual cells also are of 
larger size ; they contain numerous chlorophyll granules, which, 
if present at all in normal sporangia, are relatively few in 
number. Further, the more rudimentary the head of the 
sporangium is, the more marked is the vegetative develop- 
ment of the remaining parts. 
If pinnules showing the above characters be subjected to 
favourable conditions of heat and moisture, the vegetative 
development of the sporangia may proceed at once. On pin- 
nules laid on damp soil, and forced quickly in the propagating- 
pits at Kew, the earlier stages of this further development 
have been traced. The details show great irregularity ; and 
they are found to correspond to the greater or less complete- 
ness of arrest in the normal development of the sporangium. 
Thus, sporangia which show a clearly marked annulus do not 
usually assume any further vegetative activity ; those, how- 
ever, which are aiTested at an earlier stage in their normal 
development may produce, by a purely vegetative process, 
outgrowths of very irregular form. Sometimes all the super- 
ficial cells of the club-shaped body may take part in the pro- 
cess, and this is most clearly seen where the arrest of the 
normal development is most complete. In other cases the 
head of the arrested sporangium may be thrown off, while 
the stalk continues its vegetative growth. The result is in 
either case the formation of flattened structures, consisting 
only of parenchymatous, chlorophyll- containing cells, which, 
sooner or later, show at one or more points on their margins 
that growth with a wedge-shaped, apical cell, which is well 
known as characteristic of the Fern prothallus ; root-hairs 
are at the same time formed by the outgrowth of individual 
cells. None of my cultures have as yet formed sexual organs : 
this we must wait for; but meanwhile it may be remarked 
that Mr. Druery’s observations during the last two years 
show that, in the cases observed by him, sexual organs were 
formed, and young Fern-plants were produced by them. In 
any case, however, the above observations show that in the 
