237 
Pro that li in Sporangia of Todea. 
prothalli 1 is not a character of the species, but proves to be connected with 
germination of spores in the closed sporangium. The conditions under 
which spores germinate in a sporangium probably differ in several respects 
from those under which a free spore germinates, e. g. as regards aeration, 
water supply, and supply of inorganic salts, but there are no data for 
estimating these factors 2 . One obvious difference, however, may be pointed 
out as probably important. The spores in the sporangium must germinate 
under pressure 3 , which must increase as more spores germinate. We may 
perhaps assume (i) that the pressure prevents the prothalli from growing to 
the size that they would attain if free, and (2) that the result of this will be 
the accumulation of certain organic food-substances, which would normally 
be used or diluted in connexion with growth. High concentration of these 
substances may cause special nutrition of the protoplasm, and this may 
lead to the precocious formation of antheridia 4 . 
In experiments with Oedogoninm Klebs (’ 96 , p. 280) found that lack of 
nutritive salts (due to using only a small quantity of water for the culture) 
favoured the formation of sexual organs. In sporangia of Todea the spores 
may perhaps suffer from lack of salts owing to defective water-supply, but, 
that this factor alone will not explain the formation of dwarf male prothalli, 
is shown by the fact that free spores germinate normally in distilled water. 
The spores, moreover, probably contain a certain amount of inorganic 
reserves. Perhaps the most probable view for the spores of Todea is that 
any factor, which hinders growth without checking the accumulation of certain 
soluble organic food-substances, will favour the formation of sexual organs. 
External pressure (compression) would be one such factor, and severe 
scarcity of water 5 would be another. The result of checking growth may 
be illustrated by another experiment of Klebs (’ 96 , pp. 295-6). A species 
of Oedogoninm , which grew in soft water, showed vigorous formation of 
antheridia when transferred to an aquarium containing hard water, growth 
and division being much hindered in consequence of the amount of lime 
contained in the water. 
In sporangia of Todea the absence of antheridia on the first-formed 
prothalli is perhaps explained by the pressure of the sporangial wall being 
still insufficient. The vegetative transformations of antheridia mentioned in 
the earlier part of this paper were observed in rather old cultures, and may 
1 In the present paper the term ‘dwarf male prothalli’ refers to extremely reduced forms 
comparable to Figs. 2 and 3. 
3 Hence any explanation must at present be a matter of pure speculation. 
3 An attempt was made to imitate this condition by growing free spores in water and in gelatine 
under pressure supplied by a column of mercury, but the experiments failed ; the control cultures 
showed that the conditions were unsatisfactory. 
4 It is possible, on the other hand, that conditions other than pressure in the sporangium may 
directly favour the formation of antheridia, and hinder growth as a secondary result. 
5 Drought has been given as one of the causes of precocious formation of antheridia on prothalli 
by Woronew (’94, p. 177) and others. 
