STRUCTURAL BOTANY 



are separated by distinct internodes on the older parts, 

 but are crowded together towards the growing-points. 

 The leaves are arranged in four rows, two of which 

 spring from the lower and two from the upper side of 



the stern. The leaves on the 

 lower side are much larger 

 than those on the upper (see 

 Pig. 2). 



The arrangement, if care- 

 fully examined, is found to be 

 in pairs, each pair consisting 

 of one of the large lower 

 leaves and one of the small 

 upper ones, which are exactly 

 opposite each other. 



Each leaf bears on its upper 

 surface and close to the base, 

 a small membranous out- 

 growth, the ligule, which is 

 best observed on the very 

 young leaves (see Figs. 10 

 and 16), as it soon withers 

 and disappears. This ligule 

 is characteristic of the whole 

 genus Selaginella, and one 

 other living genus, Isoetes, and, 

 as it seems, is 



FIG. 2. SelayincllaKraussiana ; 

 young plant, m, megaspore 

 still in connection with plant ; 

 c, two cotyledons ; r, main 

 root ; r', first lateral root. 

 Note the two kinds of leaves. 

 Magnified 6 diameters. (U.S.) unimportant 



a very ancient character, for 



it is found in a large family of fossil plants of the coal 

 period (Lcpidodendrecc'). 1 



At each ramification of the stem, a root-like organ is 

 given off, which arises at the side of the stem, just below 

 the fork (see Figs. 1 and 3). These organs, the rhizophores, 



1 See Studies in Fossil Botany, p. 115. 



