306 



LYCOPODIALES 



Scotland, has been compared by Penhallow 

 with Lycopodium Selago as regards the un- 

 differeritiated shoot. 1 Without attaching too 

 much importance to the last example, it 

 appears certain that Lycopods, even of large 

 size, existed in very early times, in which 

 there was no clear differentiation of vege- 

 tative and fertile regions : in fact, the 

 " Selago " condition dates back to the 

 Primary Rocks. 



There can be no question of the Lyco- 

 podinous affinity of the fossils thus described 

 briefly in their general morphology : it 

 remains then* to indicate where the nearest 

 correspondence is to be found between 

 them and living forms. They are plainly 

 related to the Ligulate Lycopodiales, and, 

 being of a radial type of shoot, and usually, 

 if not always heterosporous, the correspon- 

 dence is nearer to the radial species of 

 Selaginella \ this suggests a comparison with 

 .5. spinulosa, from which some interesting 

 points will emerge. In the first place, the 

 difference of size is to be discounted : how- 

 ever diverse the gigantic Lepidodendron may 

 seem from the minute S. spinulosa, the com- 

 parison really relates to the relative position 

 and character of the parts composing the 

 plant-body. The parts which form the shoot 

 axis, foliage-leaf and sporophyll, the ligule, 

 and the sporangium are identical in both 

 as regards their relative positions, though 

 differing greatly in their number and dimen- 

 sions : in the dichotomous branching, and 

 in the relation of the resulting shoots to the 

 upright main axis they are alike : also in 

 the dependence of the whole plant for its 

 water-supply upon the base of the primary 

 axis. In fact, Selaginella spinulosa is like a 

 Lepidodendron in miniature, as regards the 

 scheme of its construction. The comparison 

 extends also to that curious knot which is 

 found at the base of the main axis in S. spinulosa : here the origin of the 

 roots is strictly localised : they appear endogenotisly on indeterminate 



1 Canadian Record of Science, 1892, p. 8. 



I 



FIG. 



154. 



Pleuromoia Sternbergi. Axis, with 

 the lower part of the terminal strpbilus. 

 Two-thirds natural size. After Bischof. 

 (From Engler and Prantl.) 



