60 LYCOPODIALES [CH. 



larger and in the terrestrial species /. hystrix^ the sterile leaves 

 are represented by the expanded basal portions only, which 

 persist like the leaf-bases of Lepidodendron as dark brown 

 scales to form a protective investment to the older part of the 

 stem. The innermost leaves are usually sterile; next to these 

 are sporophylls bearing megasporangia, and on the outside are 

 the older sporophylls with microsporangia. The long and 

 slender portion of the leaf becomes suddenly expanded close 

 to its attachment to the stem into a broad base of crescentic 

 section which bears a fairly conspicuous ligule (figs. 132, B, I, 

 133, E, I) inserted by a foot or glossopodium in a pit near the 

 upper part of the concave inner face. The ligule is usually 

 larger than that of Selaginella, though of the same type. The 

 free awl-like lamina contains four large canals bridged across at 

 intervals by transverse diaphragms, and in the axial region a 

 single vascular bundle of collateral structure. Other vascular 

 elements, in the form of numerous short tracheids occur below 

 the base of the transversely elongated ligule. 



Stomata are found on the leaves of /. hystrix, I. Boryana", 

 and in other species which are not permanently submerged. 

 Both microsporangia and megasporangia are characterised by 

 their large size and by the presence of trabeculae or strands of 

 sterile tissue (fig. 133, E, H, t) completely bridging across the 

 sporangial cavity or extending as irregular ingrowths among the 

 spore-producing tissue. Similar sterile bands, though less 

 abundant and smaller, are occasionally met with in the still 

 larger sporangia of Lepidostrobus ; these may be regarded as a 

 further development of the prominent pad of cells which 

 projects into the sporangial cavity in recent species of 

 Lycopodium (fig. 126, D, p). The sporangia are attached by a 

 very short stalk to the base of a large depression in the leaf- 

 base below the ligule, from the pit of which they are separated 

 by a ridge of tissue known as the saddle, and from this ridge a 

 veil of tissue (the velum) extends as a roof over the sporangial 

 chamber (fig. 133, E, v). In most species there is a large gap 

 between the lower edge of the velum and that of the sporangial 



1 Soott and Hill (00). " Motelay and Vendry^s (82) Pis. xvi, xvii. 



