HARDWICKE'S SCIENCE-GOSSIP. 



125 



or in plates giving rise to curiously-shaped patterns 

 in transverse sections. Outside all is a cellular cor- 

 tical layer, or bark. The woody cylinder " is pene- 

 trated by large open meshes, each of which permits 

 the passage of the vascular bundles which supply a 

 leaf, accompanied by a certain amount of cellular 

 tissue from the medulla which occupies the centre of 

 the mesh." "The leaves of the fern bear the fruit 

 and are hence called fronds, and the fruit is produced 

 in clusters on the back or margin of the fronds. Each 

 cluster contains many sporangia and each sporangium 

 numerous uniform spores. These spores in the least 

 as well as in the largest species are remarkably 

 uniform in size."* 



The microscopical structure of the fossil ferns 



Fig. 85. — Longitudinal section of Strobilites. 



agrees most unmistakably with that of existing 

 species. Spores are however but seldom met with 

 attached to the fronds. I have seen specimens in the 

 Owens College Museum, at Manchester. When they 

 do occur they are seen to resemble in the closest 

 possible manner those of living species in their modes 

 of attachment and general appearance. Detached 

 sporangia of the genus Hymenophyllum have been 

 found at Oldham, although the parent fronds have 

 not been recognised. When we turn to the group of 

 arborescent ferns, we find " that the vascular elements 

 of the stem form a close cylinder round the pith, 

 and the vascular bundles for the leaves are given off 

 from the out-turned edges of the cylinder when, at 

 regular intervals, co-rresponding to the positions of 



Carriithers. 



the leaves, narrow meshes occur for this purpose. In 

 another group of the Carboniferous ferns the ends of 

 the vascular plates, as seen in transverse sections, 

 turn inwards, and the leaf bundles are formed in a 

 complete condition in the axis of the stems." 



It is owing to the general absence of fructification 

 that the classification of the Carboniferous ferns is 

 attended with so much difficulty. We have almost 

 entirely to depend on the venation, or arrangement 

 of the veins in the leaflets, and this is not only very 

 varied, but there is such a gradual shading off of one 

 type into another, that to say where one genus should 

 end and another begin is almost impossible ; besides 

 this, it is a known fact that the same arrangement of 

 veins is now found in as many as five or six different 

 genera which have been determined by their 

 fructification. 



The simplest general classification as yet proposed 

 for these fossil ferns is that of M. Brongniart, which as 

 far as I am aware has not been replaced by a better. 

 He divides them into four classes, of which the 

 following are the characters : — 



1. Frond simple, or with free or adherent pinnules ; 

 no medial vein, or with a medial vein at the base, 

 but diminishing and disappearing towards the apex. 

 Venules dichotomous, flabelliform. Neuropteridse. 



2. Frond pinnate, bi-tripinnate, pinnules con- 

 tracted at the base, flabelliform, whole or slightly 

 lobed ; veins diverging from the base, mid-vein 

 not more distinct. Adiantidae. 



3. Frond, as above. Veins pinnate or bi-pinnate 

 near the base, secondary divisions very oblique. 

 Sphenopteridje. 



4. Frond simple, pinnate or bi-tripinnatifid, 

 pinnules generally adherent by their base to the 

 rachis, often confluent, and merely forming more or 

 less deep lobes, whole or denticulated without lobes ; 

 secondary veins (venules) pinnate, dichotomous, or 

 reticulated. Pecopteridce. 



There is a more elaborate classification based upon 

 this by Ettingshausen, which may be referred to in 

 Scliimper's great work on "Vegetable Palaeontology," 

 to which I am largely indebted in the compilation of 

 this paper. 



Besides the more or less perfect fronds of car- 

 boniferous ferns, there are found numerous frag- 

 ments of the rachis or steins of various species or 

 genera, such as Caulopteris, Megaphytum, Zippea, 

 and others. 



Eqiiiscfaci\r. — We must now turn to another divi- 

 sion of plants, belonging to the coal measures, the 

 Calamites ; fragments of these are very abundant, 

 and belong to several different genera. Fortunately, 

 not only is their internal structure frequently suffi- 

 ciently well preserved to enable us to examine its 

 minutest details, but the foliage and the fruit have 

 also been recovered. In appearance these plants 

 resembled gigantic Equiseta or horsetails, and there 

 can, in fact, be no doubt that it is to this order of 



