GENERAL MORPHOLOGY 299 
Phiegmaria, showing a terminal strobilus, with sporangia, and the sporophylls 
smaller than those borne by the more lax region of the shoot below (Fig. 
147). The leaves are arranged in whorls—a condition not unknown among 
species of the PAlegmaria group. The sporangia do not appear to have been 
restricted to the terminal strobilus, but to have occurred also in relation 
to the larger foliage leaves: this is a condition which has been seen 
to occur in LZ. varium, as well as in the living species of the group 
sub-Selago, from which the Phlegmaria group appear to be a specialised 
offset. So far from this distribution of the sporangia raising a difficulty, 
it seems to point to the existence in very early strata of a Lycopodinous 
type showing characters which exist in living species, and which com- 
parison indicates as primitive. These fossils are unfortunately rare, and 
in the particular case of Z. Stockit the essential facts are based upon a 
single specimen. 
B. LIGuLatTag. 
The ligulate Lycopodiales resemble the Eligulatae in general habit, 
but they differ from them in the presence of a small process—the ligule— 
borne on the upper surface of the leaf, near its base: also whereas the 
living Eligulatae are all homosporous, all the living Ligulatae are hetero- 
sporous. Seaginelia is the preponderant genus of the living Ligulatae: 
its vegetative development is characterised by frequently repeated branch- 
ing of the axis, which bears numerous small leaves: but whereas in 
Lycopodium the dorsiventral development of the shoot is the exception, 
and the radial the rule, in Se/aginella only a few species show the radial 
construction as a permanent character: the latter, as Goebel remarks,! 
usually grow on dryer and brighter spots than the dorsiventral. As 
the result of experiments on species such as S. sanguinolenta, in which 
anisophylly is not constant, but appears under the influence of external 
factors, Goebel concludes that the dorsiventrality is a phenomenon of 
adaptation brought about by light: thus the radial type will naturally 
be the more primitive. In the great majority of the living species, 
however, the strobilus is isophyllous, even where the vegetative shoot 
is anisophyllous: thus indicating that it is the more conservative part 
of the plants. But in some ten per cent. of the living species the 
strobilus itself is also anisophyllous. The definition of the strobilus from 
the vegetative shoot in Se/aginella is more marked than in Lycopodium: 
a condition corresponding to that of the Se/ago-group of Lycopodium is 
unknown, nor have isolated sporangia ever been observed in the vegeta- 
tive region: the differentiation of the sporophyte of the genus as a whole 
corresponds to that of the more specialised types of Lycopodium. But 
imperfect sporangia have been observed at the base of the strobilus of 
.S. spinulosa, and Martensit, and would doubtless be found in many 
other species: this condition is open to the same interpretation as 
1 Organography, vol. i., p. 105. 
