HIGHER LAND PLANTS 



175 



Roots: the primary root usually disappears before 

 the sporophyte matures, the mature roots forming 

 adventitiously from stem internal tissues or from 

 unique, peculiar, prop-like, equal-forking organs 

 found at underground points of stem branching (rhi- 

 zophores. Figure 11.7); roots are mostly simple, 

 sometimes equal-forking. 



Figure 11.7 /soe/es, a quillwort. A, habit (x ' o); B, rhizophore, 

 with roots and leaf bases (x 2' 2); C, sporangium-bearing leof, inner 

 surface view of base (enlarged); D, sporangium-bearing leaf, side view 

 in long section at base (enlarged); E, cross-section of leaf (enlarged); 

 I., ligule; s., sporangium; t., trabecule; v., velum; v.b., vascular bundle. 

 (Used by permission, from Arthur Cronquist, Introductory Botany, 

 Harper, 1961.) 



Reproduction: if only one single kind of spore is 

 formed, spore development ends in a gametophyte 

 having both sex organs; if tvk'o kinds of spores are 

 formed, separate male and female gametophytes of 

 highly variable form and organization develop. 



CLASS LYCOPODAE 



Diagnosis: the only recognized class; represented 

 by macrofossils since Cambrian times; characteristics 

 as for the subphylum. 



ORDER ISOETALES (Quillworfs) 



Diagnosis: known from Triassic to Recent; fossil 

 species up to 6 feet tall, composed of an erect, un- 

 branched axis upon a lobed, unbranched rootstock 

 that bore rootlets similar to those of a fossil order 

 (Lepidodendrales); upper part of axis with numerous, 



long and narrow, spirally arranged, ligulate leaves; 

 axis capped by a single, strictly male or female cone, 

 hence plants strictly male or female; living species 

 essentially "shrunk" from the fossil species to small, 

 aquatic or semiaquatic, sedge or rush-like, perennial 

 herbs; living structure consisting of quill-like, entire, 

 simple, ligulate leaves; leaves arising from an inflated 

 but flattened axis which is usually underground; 

 lower part of axis a two or three-lobed rootstock; 

 lower axis with many equal-forking roots; outer 

 leaves bearing sporangia forming female spores and 

 inner leaves bearing sporangia forming male spores, 

 but lowermost leaves sterile; sporangia occur singly, 

 on inner (upper) side of leaf between ligule and the 

 leaf base, are covered by a membrane, and are incom- 

 pletely divided by partitions; male gametophyte 

 formed within a male spore; female gametophyte 

 starts forming within a female spore, but the female 

 spore generally breaks before complete female sex 

 organ formation, so the female organ extends beyond 

 the spore confines (Figure 11.7). 



ORDER SELAGINELLALES (Spike Mosses, or Small 

 Club Mosses) 



Diagnosis: known from Pennsylvanian to Recent; 

 both fossil species and members of the single living 

 genus, Selaginella, are of much the same appearance; 

 certain fossil species produced seed-like structures 

 but not true seeds; modern forms are mostly smaller 

 than fossil taxa and resemble club mosses, mostly 

 perennial herbs, a very few delicate annuals; some 

 are erect and shrubby; others are prostrate creep- 

 ers that form tufts, mounds, or mats and resemble 

 mosses, but have roots; some are fern-like and have a 

 conspicuous underground stem (rhizome); leaves are 

 mostly less than J^-inch long, spirally arranged, 

 sometimes in four distinct rows, and ligulate; roots 

 grow from leafless root stocks; sporangia always de- 

 velop in cones; two kinds of spores; male gametophyte 

 forms completely within male spore; female gameto- 

 phyte essentially as in Isoetales (Figures 11.8 and 

 11.9). 



ORDER LYCOPODIALES (Club Mosses) 



Diagnosis: known from Pennsylvanian to Recent; 

 ours mostly trailing or creeping, also erect, perennial 

 herbs; somewhat moss-like, general form of some 

 causes them to be called "ground pines"; branching 



