284 Bower,— Some Normal and Abnormal 
The gemmae of Trichomanes alatnm are borne in the 
greatest profusion on the ends of the prothalloid growths. 
They may appear on those strap-shaped growths which are 
borne on the tips of the pinnae (Fig. 30), or at the ends of the 
secondary expansions (Fig. 25), or even in some cases they 
may be the product of simple filaments (Fig. 40), though this 
is less common. There is no reason to think that the gemmae 
borne in these different positions differ in the least in their real 
nature. Their development is in the following manner. 
Single cells of the prothallus assume first an elongated form 
(Fig. 41 [i]), becoming very soon enlarged at the apex into a 
spherical head (Figs. 41, 43 [ii]) ; this is subsequently cut off 
by a septum (Figs. 30, 41, 42 (iii]), the lower cell being the 
pedicel or sterigma, and the upper, or head, developing into 
the gemma ; this now elongates transversely, or it may be in 
an oblique direction, and undergoes successive divisions by 
walls perpendicular to the axis of elongation (Figs. 30, 41, 42 
[iv]), till the whole gemma is ultimately composed of five to 
seven cells ; these become slightly barrel-shaped at the period 
of maturity, and are densely stored with reserve materials. 
Meanwhile a change takes place in the upper part of the 
sterigma ; the cell-contents are for the most part transferred 
to the gemma, while a brown coloration of the wall appears 
near the apex. At this point the wall appears to be very 
brittle, and it is here that the gemma breaks away, often 
carrying with it a small portion of the sterigma {x Figs. 43, 
44), which may still be recognised after germination has 
begun. When sown on damp soil, and kept at a moderate 
temperature, the germination of the gemmae is excessively 
slow ; for instance, I have seen gemmae which have been culti- 
vated on damp soil for six weeks remain quite unchanged, 
though still of healthy appearance. Owing to this very slow 
development I am not in a position to go further than to 
state that germination does take place (Fig. 44). 
After a sterigma has produced a single gemma its function 
is over, and it does not develop further, but remains adherent 
to the prothallus, such old sterigmata being often seen in very 
