2 33 
Prothalli in Sporangia of Todea. 
same pinnule) as the closed sporangia used in the same experiment, and 
the two cultures were placed side by side in a greenhouse, Petri-dishes being 
used in most cases. The temperature of the greenhouse varied considerably, 
but during the day-time, in some or most of the experiments, was usually 
between i6° and 21° C. One experiment including several cultures was set 
up as follows. Free spores were kept (i) on damp blotting-paper, (2) on 
damp sand, (3) immersed in water in a watch-glass. Three parallel cultures 
were made, using detached closed sporangia instead of spores. These were 
all exposed to daylight, and a similar set of six cultures was kept in dark- 
ness (in a light-tight box). To these were added pinnae bearing sporangia, 
and placed on damp blotting-paper in light and in the dark. This experi- 
ment was carried out both in T. Fraseri and in T. hymenophylloides , and 
some of the pairs of cultures were repeated two or three times. 
The general result obtained was that dwarf male prothalli with anthe- 
ridia were found in several of the sporangia, but were never produced by 
the germination of free spores. From an examination of the contents of 
the sporangia, it was evident that, under the conditions of the experiments, 
a certain number of dwarf prothalli with antheridia were formed in the 
sporangium whenever the germinative power of the spores was sufficiently 
strong, and the culture could be kept healthy long enough. Their formation 
is thus connected with germination inside the closed sporangium, and this 
again is due to excessive dampness, which prevents the sporangium from 
dehiscing when mature. This was shown by uncovering a Petri-dish con- 
taining a pinna with sporangia on damp blotting-paper. A few minutes’ 
exposure to dry air, if the culture was not too damp, was sufficient to cause 
normal dehiscence of several sporangia. 
Figs. 3 and 4 are examples of dwarf gametophytes from closed 
sporangia, which had been kept damp in the light for twenty-one days. 
They are shown in optical section, with the cell-contents omitted (as in 
most of the figures), a. being the cavity of the antheridium. It will be seen 
that Fig. 3 is very similar to Fig. 2, described above, but differs in the 
presence of a rhizoid-cell (r. c .), while Fig. 4 has no rhizoid-cell, and is 
exceptional in having a rudiment of a lateral branch (/.), which, from com- 
parison with another specimen, may have been destined to form a second 
antheridium. 
Sporangia which fail to dehisce behave alike when exposed to light, 
whether they remain attached to the living plant, or to a pinnule kept 
damp on blotting-paper, or whether they are detached and similarly 
treated ; at any rate no marked difference in the germination of the spores 
was noticed. Under favourable conditions a number of spores germinate, 
and some of them produce dwarf prothalli and antheridia h The prothalli 
1 In the case 01 sporangia immersed in water, germination was usually not very satisfactory t 
perhaps owing to defective aeration. 
R 
