Pteridophytes . Are they vestigial? 245 
that the whole leafy plant in the mature state is potentially, 
as it is in these actually, fertile. Attention is then thrown 
back to embryonic plants, and the question arises, how early 
may the sporangia make their first appearance on the young 
sporophyte ? 
We have as yet no information as to the embryology of 
any of those extreme forms where sporangia are borne down 
to the base of the mature plant ; and indeed of the whole 
Selago group, with its comparatively undifferentiated sporo- 
phyte, it is only in one species that the embryonic details 
have been observed, viz. in L. Selago. Bruchmann 1 has 
given an account, with drawings, which supplies the facts. 
The prothalli of this species may be either buried in the soil, 
or superficial, in which latter case they may be deep green. 
But Bruchmann 2 remarks that ‘ it appears to be of great 
advantage to the seedlings, which are not adapted for an 
underground growth, to arise as near to the surface of the 
soil as possible, so that their first leaves may easily reach the 
daylight. 5 This species then is not one of those specialized 
cases like L. clavatum 3 , and L. annotinum , with deeply buried 
prothallus, but more nearly shares with L. cernuum and L. 
inundatum what was probably the primitive state, viz. with 
a superficial, chlorophyll-containing prothallus. Bruchmann 4 
figured a large number of varying cases of the prothalli of 
this species, at different levels : some at the surface of the 
soil, others below, with their seedlings attached; and from 
these, together with his text, certain important facts emerge. 
The first period of development of the embryo, that is the 
initiation of the fundamental structure of the germ inZ. Selago , 
corresponds to that in other species of the genus 5 : but in 
1 Ueber die Prothallien und die Keimpflanzen, &c., Gotha, 1898, p. 97, PL VI, 
VII. 
2 Loc. cit., p. 85. 
* For an additional description of the facts for L. clavatum , together with an 
excellent comparative discussion of the prothallus and embryo in other species, 
from the biological point of view, see W. H. Lang, Annals of Botany, vol. xiii, 
P- 2 79* 
* Loc. cit., PI. VI, Figs. 1-26. 
5 Bruchmann, loc. cit, p. 98. 
