208 SYMMETRY OF THE SPOROPHYTE 
In the Gymnosperms the radial type is constant as a whole for the 
cones, both male and female; but, as in Welwztschia, there may be a 
more or less marked zygomorphy in the individual flowers. 
In the strobiloid Pteridophytes also the strobili are for the most 
part of radial construction. In the Equisetineae this is the case with- 
out exception; also in the Sphenophylleae, so far as they are known. 
The related Psilotaceae are also radial in their fertile region, with the 
exception of the pendent species Ps. complanatum, Sw., which is isobi- 
lateral, probably as a secondary modification in accordance with its pendent 
habit: it bears its leaves and synangia only on the margins of the 
flattened branches. In the genus Lycopodium the strobili are always 
radial, even where the vegetative shoot is strongly dorsiventral- But 
in Seaginella, though the large majority of species show a radial strobilus, 
even where the vegetative shoot is dorsiventral, still the subgenera 
“Homostachys” and ‘“Heterostachys” have dorsiventral strobili. The 
conclusion that these are derivative seems in this case unavoidable. 
Isoetes, and the fossil Lycopodinous genera have all radial strobili. Even 
Ophioglossum and Botrychium may be held to be of the same type, 
their upright axis in the polyphyllous species bearing leaves of equal 
size on all sides; but in the monophyllous species only one of these 
is as a rule expanded at one time; still, excluding the factor of time, 
the type of arrangement is radial of the shoot asa whole. Helminthostachys, 
however, is dorsiventral as regards the whole shoot; and this may well 
be held, on comparison with the other genera, to be a derivative 
condition. 
The case of the Ferns, including the Hydropterideae, is not so readily 
brought into line with the strobiloid forms, owing to the sori and 
sporangia being distributed widely over their large leaf-surfaces and 
margins, while the sporophyils frequently show no differentiation in form 
or position from the foliage leaves. Their condition will be more fully 
considered later; meanwhile it may be pointed out that, within definite 
circles of affinity, a radial conformation is seen in upright forms, similar 
to that in strobili of other Pteridophytes, while those with oblique or 
horizontal axis show dorsiventrality, such as is seen in the strobili of 
certain Selaginellas and in Aelminthostachys. Thus, though no definite 
strobilus is present, the relations of symmetry of the fertile. shoot in 
Ferns are still comparable with those in other Pteridophytes. 
Thus a review of the strobili of Pteridophytes as a whole leads to 
the recognition of a very great prevalence of the radial symmetry in 
them. In several large groups, which are certainly primitive in character, 
being represented early in palaeophytological history, the radial type of 
strobilus is never departed from: in others only occasionally; and this 
radial character of the strobilus may even persist in cases where the 
vegetative system shows dorsiventrality. 
An examination of vegetative shoots of vascular plants at large shows 
