238 Boodle. — On the Production of Dwarf Male 
have been due to a change in the conditions inside the sporangium, caused 
by the collapse of some of the prothalli, often observed in old cultures. 
In many Ferns it is well known that, when spores are sown crowded, 
the prothalli remain small and produce antheridia only k This is somewhat 
similar to the formation of dwarf male prothalli in Todea , but such extreme 
reduction of the prothallus as that shown by Todea has not often been 
observed. For the Osmundaceae, Luerssen ( 74 , p. 469) states that the 
antheridia often appear on very young prothalli, but in the only figure he 
gives of an antheridium on a complete prothallus the latter consists of 
twenty-six or more cells. Borodin (’68, p. 438) describes dwarf male 
prothalli in Allosurus ; these will be referred to later. Schacht (’ 49 , pp. 756, 
787, Taf. v, Fig. 1) describes extremely small prothalli bearing antheridia 
in P teris serrulata 2 , and his figure shows a case in which only an antheridium 
and two other cells are present, viz. a short cell containing chlorophyll, and 
a rather well-developed primary rhizoid. Cornu (’ 74 , p. 161) describes 
similar prothalli (of two cells and an antheridium) in N ephrodium Filix-mas. 
In these two cases the degree of reduction is similar to that found in Todea. 
Woronew (’ 94 , p. 177) also describes the formation of antheridia on reduced 
prothalli (of three or four cells) under unfavourable cultural conditions. 
Regarding the power of Fern-spores to germinate in the dark, the 
earlier statements are contradictory. Thus Borodin (’68, p. 432) and Kny 
( 72 , p. 4) described light as necessary for germination, while Schelting 
( 75 , p. 328), experimenting with spores of four species of Anemia , Pteris , 
and Aspidium , found that they all germinated in the dark. Beck ( 78 , p. 780), 
however, found that spores of Scolopendrium vidgare would only germinate 
in the light, and Woronew (’ 94 , p 176) failed to germinate spores of 
ordinary Ferns in darkness, but succeeded with those of Pilularia and 
Marsilia. Heald (’ 98 , p. 43) found that in Ceratopteris thalictroides the 
spores refused to germinate in the dark at a temperature of 19 0 to 21 0 C., 
though germinating in light at this temperature, but that at 32° C. they 
germinated well in darkness. He regards the conflicting results of earlier 
authors as probably explained by assuming that unsuitable temperatures 
were used in some of their experiments. Heald only experimented with 
one species of Ceratopteris and one of Alsophila , hence it is unsafe to 
1 Goebel (’82, p. 198). Millardet (’69, p. 50), referring to prothalli bearing antheridia only, states 
that in one entire sowing of Osmunda regalis he could not find a single archegonium. Prantl (’78, 
p. 499) found that the production of archegonia was connected with meristematic growth of the 
prothallus, inasmuch as reduced prothalli with no meristem (‘ ameristic prothalli’) bore antheridia, 
but never archegonia. He attributes the ameristic condition to insufficient nutrition, light or water 
(and especially the dissolved mineral salts), but sometimes refers it to the nature of the spore itself. 
In a later paper Prantl (’81, p. 753) showed that absence of nitrates in the nutrient solution conduced 
to the formation of ameristic prothalli. Sadebeck (’79, p. 166) points out that the tendency to 
dioecism ascribed to Ferns is explained in most cases by the fact that certain prothalli have 
remained ameristic. 
2 In this species dwarf prothalli bearing antheridia are also described by Atkinson (’94, pp. 15, 16). 
