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 . spinulosa, 

 specially investigated by Bruchmann : x 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 Selaginellas may be 

 regarded as specialised offsets from some such radial type as this. The 

 seedling of 6". spinulosa 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 

 which certain stronger branches are 



Selaginella spinulosa. G=young seedling . ., , ., /T -,. x ,. 



with megaspore attached, showing elongated fertile, the TCSt Sterile (Fig. 149). The 

 hypocotyl (H) and cotyledons K. ff= seedling f ,1 i r .1 



more advanced showing dichotomy. ^=base arrangement of the leaves of the primary 



of hypocotyl with swollen knot. W= roots. j 



^hypocotyl. .ff^suspensor (after Bruch- aXIS IS deCUSSate, but On the later 



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 Selaginella^ 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. 2 



1 Unters. iiber S. spinulosa, A. Br., Gotha, 1897. 



2 See Goebel, Organography, vol. ii., p. 230. 



