EMBRYOLOGY 343 
which the prothalli grow, and they are attached by hairs which project 
in all directions. Here again a fungus plays an important part in the 
nutrition, which is exclusively saprophytic. The prothalli reproduce readily 
by gemmae, as also by progressive decay, which separates the ultimate 
branches as distinct individuals. The sexual organs are borne upon the 
upper surface of enlarged branches of the thallus, and are always accom- 
panied by paraphyses. 
Such different types of prothallus, when studied separately, appear 
widely divergent: and at first the underlying unity of their construction 
was less appreciated than the differences which they show; so little indeed 
that Bruchmann, to whose labours so many of the important facts are 
due, was disposed to make those differences the basis of a division of 
the genus Lycopodium into distinct groups, or even genera.! But Lang, who 
had simultaneously with him been 
at work on the prothallus of Z. 
clavatum,*? pointed out clearly the 
relation of the divergent types 
to one general plan, recognising 
especially how the prothallus of 
L. Selago, one of the species 
described by Bruchmann, gives 
the clue to their connection. For Fic, 180. 
its prothallus appears to be variable Prothalli of Lycopodium Selago, bearing seedlings. 
a, 3 o, o shows the level of the soil, and the seedlings in their 
in its mode of development (Fig. development show varying proportions so that the first 
180). It is usually a pale under- ered al be exposed above ground. (After Bruch- 
ground body; but at other times 
it grows above ground, and is coloured a full green. The spores appear to 
germinate either at the surface or below it. The form of the prothallus is 
determined largely by the soil in which it develops: thus; the elongated 
cylindrical form is usually found in firm ground, though less deeply 
buried than in the aznotinum-type: the thallus seems, in fact, to stretch 
upward as though to bring as near to the surface as possible the seedling 
unsuited for subterranean growth. The subterranean prothalli may be 
simple, or be branched so as to take a coral-like form. In more open 
soil, however, and especially near to the surface, the prothalli are more 
compressed and flattened. Each prothallus tapers off as in the other 
types at its lower end into a conical point, which indicates where it 
issued from the spore, while towards its upper end the sexual organs are 
formed. In the half-saprophytic prothalli, grown to the surface of the soil, 
the conical form similar to that of other types is clearly seen (Fig. 181): the 
saprophytic lower region, the meristem, and the crown bearing the sexual 
organs and paraphyses holding the usual positions. 
1 Ueber die Prothallien und die Keimpflanzen mehrerer europaischen Lycopodien, 
Gotha, 1898, p. 108. 
2 Annals of Botany, xiil., p. 279. 
