1 66 HISTORICAL PALEONTOLOGY. 



in the Carboniferous deposits, and have given occasion to an 

 abundance of research and speculation. They present them- 

 selves as prostrate and flattened striated stems, or as similar 

 uncompressed stems growing in an erect position, and some- 

 times attaining a length of twenty feet or more. Externally, the 

 stems are longitudinally ribbed, with transverse joints at regular 

 intervals, these joints giving origin to a whorl of branchlets, 

 which may or may not give origin to similar whorls of smaller 

 branchlets still. The stems, further, were hollow, with trans- 

 verse partitions at the joints, and having neither true wood nor 

 bark, but only a thin external fibrous shell. There can be little 

 doubt but that the Calamites are properly regarded as colossal 

 representatives of the little Horse-tails (Equisetacece) of the 

 present day. They agree with these not only in the general 

 details of their organisation, but also" in the fact that the fruit 

 was a species of cone, bearing " spore-cases " under scales. 

 According to Principal Dawson, the Calamites " grew in dense 

 brakes on the sandy and muddy flats, subject to inundation, 

 or perhaps even in water ; and they had the power of budding 

 out from the base of the stem, so as to form clumps of plants, 

 and also of securing their. foothold by numerous cord-like roots 

 proceeding from various heights on the lower part of the 

 stem." 



The Lepidodendroids, represented mainly by the genus 

 Lepidodendron itself (fig. no), were large tree-like plants, 

 which attain their maximum in the Carboniferous period, but 

 which appear to commence in the Upper Silurian, are well 

 represented in the Devonian, and survive in a diminished form 

 into the Permian. The trunks of the larger species of Lepido- 

 dendron at times reach a length of fifty feet and upwards, giv- 

 ing off branches in a regular bifurcating manner. The bark 

 is marked with numerous rhombic or oval scars, arranged in 

 quincunx order, and indicating the points where the long, 

 needle-shaped leaves were formerly attached. The fruit con- 

 sisted of cones or spikes, carried at the ends of the branches, 

 and consisting of a central axis surrounded by overlapping 

 scales, each of which supports a " spore-case " or seed-vessel. 

 These cones have commonly been described under the name 

 of Lepidostrobi, In the structure of the trunk there is nothing 

 comparable to what is found in existing trees, there being 

 a thick bark surrounding a zone principally composed of 

 "scalariform" vessels, this in turn enclosing a large central pith. 

 In their general appearance the Lepidodendra bring to mind 

 the existing Araucarian Pines ; but they are true " Crypto- 

 gams," and are to be regarded as a gigantic extinct type of the 



