Prothalli in Sporangia of Todea . 235 
the experiments, and it is probably in consequence of this, that fully formed 
antheridia were only rarely found in cultures of closed sporangia of 
T. hymenophylloides . In several cases the cultures became unhealthy before 
germination was sufficiently far advanced. Figs. 8 and 9 are prothalli from 
a closed sporangium after thirty-two days in the light. In Fig. 9^ no 
antheridium has been formed, while in Fig. 8 an abnormal antheridium, 
in which the cavity (a.) contains chlorophyll, is borne by a very rudimentary 
prothallus. The presence of a rhizoid (r.) in this type of prothallus is not 
common. In Fig. 10 (also from a closed sporangium of T. hymenophylloides ) 
the form of the cells indicates that the prothallium had made an abortive 
attempt to form an antheridium. Several similar examples were seen in 
T. hymenophylloides in closed sporangia. In these, two or more cell- 
divisions had taken place, cutting off cells similar to those which normally 
go to form the antheridium, but the cells generally retained their chlorophyll, 
and sometimes became enlarged. 
Examples of well-advanced prothalli grown from free spores on 
blotting-paper in the light are given in Figs. 11 and 12. Fig. 11 is from 
a spore of T. Fraseri after thirty-six days. The rhizoid (r.) is rudimentary 
in this specimen, and, as often occurs when the rhizoid is reduced, its wall 
is thickened in the form of a cap at the apex. Fig. 12 is from a spore of 
T. hymenophylloides after thirty-two days, and may be compared with 
Figs. 8 and 9, which are prothalli from a sporangium in a culture of 
the same age. 
Some experiments of a different kind may now be referred to. Firstly, 
germination of free spores in distilled water and tap-water 1 was compared, 
and it was found that the spores germinated more rapidly in distilled water. 
Figs. 13 and 14 are from cultures of spores of T. Fraseri in light after three 
days. In Fig. 13 (in tap-water) the spore has burst its exosporium ( e.) t 
but probably remains undivided, while in Fig. 14 (distilled water) the 
exosporium has been thrown off, and the young prothallus consists of three 
cells including a fairly long rhizoid. These specimens were grown in watch- 
glasses with the water about 2 mm. deep 2 . P'or the growth of the pro- 
thallus, distilled water has the advantage for some time, but in one 
experiment after fourteen days the prothalli in tap-water proved to have 
slightly outstripped those in distilled water as to length 3 * . In distilled 
water the rhizoid is usually well developed. 
Germination in 5 per cent, solution of cane-sugar gave slower growth 
of the prothallus than in tap-water, and the rhizoids were short. 
A number of cultures were started in water in upright glass tubes (4 mm. 
diameter), but these need not be described further, as several of these 
1 Rather hard water. 
2 The rate of germination depends to some extent on the depth of the liquid, the relation 
being inverse. 8 This refers to the length of the prothallus, excluding the rhizoid. 
R 2 
