2 9 
Anatomy of the Genus Selaginella , Spr. 
first to seek an independent mechanism for these spores. I have not been 
able to discover one, and any such variation from the rule can easily be 
explained, as will be shown later.) 
Whilst this change is taking place in the flaps, the boat-shaped portion 
has altered considerably. The sides, which were at first strongly convex, 
straighten out and approximate to each other, this process being facilitated 
by the thin tissue connecting the valves assuming a convex, instead of 
retaining its original concave, form. It is on this account described by 
Goebel as a ‘ hinge ’, whose function is to permit the elongation of the basal 
boat-shaped portion. The gradual approximation of the two lower walls 
(due to the thin outer walls of the active cells becoming concave) exerts 
a pressure on the two lower spores, and they are gradually squeezed out¬ 
wards, the sporangium then appearing as represented in PI. Ill, Fig. 3. 
Finally, they are shot out by the total collapse of the basal walls, just 
as a cherry-stone when pressed between the thumb and forefinger, to use 
Goebel’s comparison. This rapid closing of the lower walls has a definite 
effect on the passive upper flaps, by which means they are jerked towards 
one another, and the spores lying on them, and only delicately balanced, 
are shed, simultaneously with the lower spores. After shedding of the 
spores, the basal portion of the sporangium is still open, and the flaps gape 
widely. The sporangium recovers its shape quickly on placing it in water, 
and will repeat the same vigorous movements again on drying. In cases 
where the two upper spores are shed first, this is due to a preliminary jerk 
on the part of the lower part. The pressure exerted by the approaching 
lower walls causes a slight movement in the upper flaps, and a consequent 
shooting of the upper spores. 
A complete splitting of the sporangium down to the stalk sometimes 
occurs immediately after the spores have been shed. This is not, however, 
the normal method of procedure. The upper flaps have no independent 
power of shooting their spores ; the thickening of the sporangium wall 
is therefore concentrated in the lower part. 
Such an elaborate contrivance as that described for the megasporangium 
is unnecessary in the case of the microsporangium, for the spores, when 
once exposed, may easily be distributed by the wind. As a result there is 
here no definite ‘ hinge region ’, neither is the thickening confined to the 
basal portion, but occupies the central region of each valve (PI. IV, Fig. 7), 
and is sometimes, as in S. Kraussiana (PL IV, Fig. 6), of a characteristic 
nature. A median longitudinal section of the microsporangium (PI. IV, 
Fig. 10) shows that these cells again are identical in structure with those of 
the fern annulus, and of the basal portion of the megasporangium. They 
are arranged in approximately transverse rows, whilst those of the thinner 
marginal region are parallel to the edge of the valve. The two valves are 
prevented from splitting down to the stalk by the thickened basal portion 
