300 LYCOPODIALES 
in Lycopodium. As is well known, the megasporangia and microsporangia 
are alike in their early stages of development, though differing later in 
the spores which they produce: this additional degree of differentiation 
in the genus falls in with the higher differentiation noted in the vegetative 
organs, as compared with Lycopodium. 
Of the species with radial construction, the best known is S. spmulosa, 
specially investigated by Bruchmann:! this will be briefly described for 
purposes of comparison on the one hand with Lycopodium, and on the 
other with the related fossils, while the dorsiventral Se/agine//as may be 
regarded as specialised offsets from some such radial type as this. The 
seedling of S. spcnulosa is like other Selaginellas in having an upright 
elongated hypocotyl (Fig. 148), which is continued directly into the primary 
root: the hypocotyl bears two cotyledons, after which a variable number 
of pairs of epicotylar leaves are formed 
before the first branching, which is a 
true dichotomy. The limbs thus formed 
branch repeatedly, at first dichotomously, 
but later monopodially, all the branch- 
ings being in one plane, at right angles 
to that of the first dichotomy: thus two 
fan-like branch-systems are produced, of 
pees Seca Be eiteeesie which certain stronger branches are 
with megaspore attached, showing elongated fertile, the rest sterile (Fig. 149). The 
hypocotyl (7) and cotyledons K. A’=seedlin . 
more advanced showing dichotomy, Fobase arrangement of the leaves of the primary 
pI eels aly aetna wee axis is decussate, but on the later 
mann), 47 —netnral ee, 2 Ge enlarses. branches there are transitions to spiral, 
while in the thicker strobili the arrangement is on a complex spiral 
plan. The main axis terminating below in the hypocotyl remains 
permanent, and its base swells at the level of the suspensor to form a 
knot, from which alone the later roots originate; they are formed 
endogenously in swellings of tissue of the knot, and burst their way 
outwards through the superficial tissue. The whole plant of S. spinulosa 
is thus dependent upon a central source of water-supply from the base 
of the main axis. In most species of Se/aginella, however, the well- 
known rhizophores are formed, at the branchings of the axes of higher 
order, and thus their rooting may be efficiently carried out at a distance 
from the primary axis: this is probably a derivative condition, just as 
the dorsiventral development, of which it is the usual concomitant, is 
also derivative. Both in the form of the shoot, and in the central root- 
ing, the type of S. spinulosa may be held to be more primitive than 
the common dorsiventral type of the genus: in these respects it will be 
seen to correspond more nearly with the large fossils than do the more 
specialised species of the genus.? 
1 Unters. tiber S. spinulosa, A. Br., Gotha, 1897. 
2See Goebel, Organography, vol. ii., p. 230. 
