HARDWICKE'S SCIENCE-GOSSIP. 



61 



Stigmaria and other Lepidodendroid plants, and also 

 in modem Dicotyledonous plants. These rays vary 

 in size, from one or two to six or more rows of cells. 



and outer bark. The innermost portion of the inner 

 bark is composed of cellular tissue of a very delicate 

 character, which is known as the pseudo-cambium. 



Fig. 48. — Tangential section of fibrous layer in Lyginodendron (mag. 8 diameters). 



Fig. 49.— Ironstone cast of Lyginodendron (nat. size). 



The bark : this part of the plant is a most peculiar 

 and highly characteristic structure. It may be 

 divided into three portions ; namely, inner, middle, 



layer. This layer, however, is rarely preserved in 

 the fossil state, although it occurs in several of my 

 specimens. The remainder of the inner bark (/) is 

 composed of larger cells, with thicker walls. The outer 

 bark is also formed of similar cellular tissue to the last 

 named, but is very rarely seen ; indeed the whole of the 

 true epidermal layer has not yet been found attached 

 to the plant, that I am aware of. The middle layer 

 (g) is the most characteristic feature about the bark, 

 and, on account of its almost indestructible character, 

 it is nearly always more or less preserved. It is com- 

 posed of a series of fibrous bands, formed of dark- 

 brown tissue, and so dense in structure as to appear 

 like black lines. These bands are of pretty uniform 

 length, but very irregular in outline, so that they 

 appear not unlike Roman numerals, which give to 

 transverse sections of this plant a striking resemblance 

 to a clock face. These dark bands are composed of 

 true fibrous vessels, which appear round in transverse 

 sections, but are seen to be long and fusiform in 

 longitudinal ones. Tangential sections (fig. 48) show 

 that these bands ascend the stem in an undulating 

 manner, and interlace with one another, thus en- 

 closing large lenticular spaces and giving to these 

 sections an appearance not unlike that presented by 

 cortical sections of Lepidodendron. But there is 

 really no affinity between the two sets of tissues, for 

 while the latter tissue is cellular, the former is true 

 woody fibre. I have in my cabinet some large 

 cortical sections of Lepidodendron obovatum in which 

 the leaves have lost their raised central portion and 



