146 SPORANGIOPHORES AND SPOROPHYLLS 
the same median plane, and, excepting rare abnormalities, each sporophyll 
subtends only one sporangium: this is seen in all plants belonging to 
the Lycopodiales. But they illustrate various degrees of remoteness of 
the sporangium from the axis, while still retaining the strict numerical 
and subtending relation. Thus Se/agine/la shows the closest relation of 
the sporangium to the axis; but the sporangium of Lycopodium originates 
clearly from the tissue of the sporophyll itself (Fig. 75): in some of them 
(Z. Seago) the sporangium may at maturity appear to be thin-stalked 
and axillary, while in others (Z. clavatum, Lepidostrobus, and Jsoetes) the 
sporangium may extend with a broader base some considerable distance 
along the upper surface of the sporophyll. An extreme condition is that 
Fic. 74. Fic. 75. 
Selaginella Martensii, Spring. Radial Radial sections through young sporangia of Lycopodium 
section of a strobilus, including apex (a), Selago. In the youngest the whole sporophyll is shown (2), 
and traversing a young sporophyll (¢), and @ and the axis (s¢), and it is seen that the sporangium arises 
sporangium (7). Also another section of upon the surface of the sporophyll. X 200. 
sporophyll and sporangium, rather older. 
X 365. 
of the early fossil Spencerites (Fig. 76), in which the narrow-stalked 
sporangium is attached some distance from the base of the sporophyll. It 
is thus seen that while the numerical and radial relations of sporangium 
and sporophyll are constant, the distance of the sporangium from the axis 
may vary. This arrangement in the Lycopods, which dates back to the 
earliest fossil records, is certainly the simplest seen in the cones of 
Pteridophytes, and the relation of the sporangium to the axis is habitually 
closer in them than in any other type. 
But other plants, which also have representatives of palaeozoic age, 
bear cones of more complex construction: these present intricate morpho- 
logical problems if the effort is made to classify their parts according to 
the strict categories and the usual successions of axis, leaf, emergence, 
and sporangium; for instance, the modern Psilotaceae and the ancient 
