356 LYCOPODIALES 
(B) LIGULATE LYCOPODIALES. 
It is an unfortunate circumstance that the embryogeny of fossils is 
usually inaccessible, for that of the dendroid Lycopods would greatly 
strengthen views as to their relation to modern forms. As it is, Seda- 
ginella and Tsoetes provide the only facts of the embryogeny in the 
Ligulate Lycopods: it will be seen that they are strangely divergent in 
the form of the embryo. 
It has been pointed out that Selagznella spinulosa may be held to 
be more primitive as regards the morphology of the mature plant than 
the dorsiventral species of the genus; and further, it has been seen that 
it differs from them anatomically, showing a vascular structure which is 
probably more primitive also. This gives a special interest to its em- 
bryology, which has been fully worked out by Bruchmann.! The early 
stages are essentially as in Lycopodium, resulting in a suspensor, and two 
tiers of four cells each, forming the embryo: the whole structure is at 
first straight, with the apex flattened (Fig. 190 a, B). The suspensor 
remains as in Lycopodium, and is a means of thrusting the embryo down- 
wards into the tissue of the prothallus. The lower tier of cells of the 
embryo (z.¢. that between walls 1, 1. and Iv., Iv. in Fig. 190 a and c) itself 
forms the hypocotyl, which may here be greatly elongated and curved. 
and becomes thus a prominent featuré of the embryo; at its base, in 
close relation to the suspensor, the first root arises in a lateral position. 
The products of the upper tier at first remain small (¢e. above wall 
Iv., Iv., Fig. 190 A, Cc): the formation of the first cotyledon may in some 
cases be long delayed, sometimes it may still be wanting even when the 
axis has already curved obliquely to the suspensor. The second cotyledon 
may be even longer delayed: in some cases it only appears after the shoot 
issues from the spore But sooner or later two opposite but unequal 
cotyledons successively make their appearance. Their orientation relatively 
to the suspensor is liable to vary. The apex of the axis, which has no 
single initial cell, lies between them, originating from the centre of the 
flattened apex of the embryo (Fig. 190 4, c, D). As the- hypocotyl 
elongates the embryo curves so that the axis takes a vertical position, while 
the suspensor is pushed to one side by the growing root. Finally the 
shoot emerges above ground, and the two cotyledons, developing at last 
to equal size, appear as green assimilating leaves (Fig. 190 G, H). 
According to Bruchmann, no enlarged “foot” is formed in this species, 
and the same appears to be the case in Se/aginella apus. 
Comparing this embryogeny with that so well known in S. Martensit, 
there is essential similarity in the disposition of the parts. The chief 
difference lies in the presence of an haustorial swelling of the hypocotyl 
in S. Martensiz, which has been called a “foot,” and in the fact that 
single initials are found at the apices of stem and root: this accords 
1 Unters. ueber “‘ Selaginella spinulosa,” Gotha, 1897. 
