HARD WICKE'S SCIENCE- G OS SIP. 



99 



little plants known as Rhizocarps, or Pepperworts, 

 which are usually placed near the Ferns, but which 

 in many respects have affinities with higher forms. 

 A typical species of Pepperwort {Jlfarsilea fahri) 

 has a creeping stem sending rootlets downwards, 

 and long stems bearing clover-shaped leaves upwards. 

 The fructification is at the base of the leaves in the 

 shape of ovoid sacs called sporocarps, and in each 

 sporocarp microsporangia and macrosporangia are 

 formed. [Microsporangia are now considered as 

 the homologues of the pollen, and macrosporangia as 

 the homologues of the ovules of higher plants.] The 

 Rhizocarps of Devonian times have a history almost 

 as curious as that of the Foraminifera of the Chalk. 

 There is every reason to suppose that their spore 

 cases, known as sporangites, form the chief source of 

 the abundant reservoirs of petroleum and natural gas 

 in the United States and elsewhere. The sporangites 

 are highly bituminous, and contain, like the spores of 

 Lycopods, nearly twice as much carbon as cellulose, 

 or the ordinary tissue'of plants : — 



Cellulose, C 24, H 20, O 20. 

 Lycopodium, C 42, H 19 fj NO 5 ■^. 

 Their distribution over the earth's surface is im- 

 mense ; they are found in North America, in Brazil, in 

 Germany, in England, and in the "white coal" of 

 Australia and Tasmania. 



The oldest bed of spore-cases examined£by Sir J. 

 W. Dawson, is at Kettle Point, Lake Huron. It is 

 a "bed of brown bituminous shale, burning with 

 much flame, and under a lens is seen to be studded 

 with flattened disc-like bodies, scarcely more than a 

 hundredth of an inch in diameter, which under the 

 microscope are found to be spore-cases (or macro- 

 spores), and in the same shale are found vast numbers 

 of rounded, translucent granules, which may be 

 escaped spores (microspores)." 



In comparing these fossil spore-cases with those 

 of modern Rhizocarps, they are found to be perfectly 

 analogous with the spore-cases of Salvmia iiatans, a 

 modern European species. In the bed at Kettle 

 Point are found fossil Calamites and Lepidodendra, 

 whose spores are, however, totally different to those 

 of the Rhizocarps. These plants probably drifted to 

 the spot where they are found imbedded, as the bed 

 itself is marine, containing the graceful sea-weed 

 Spirophyton and shells of Lingula. Some years 

 after the discovery of the Kettle Point beds, immense 

 deposits were found extending throughout the black 

 shales of Ohio, from the Huron River on the shore 

 of Lake Erie, to the Ohio Valley, a distance of nearly 

 two hundred miles. 



The beds are from ten to twenty miles in breadth, 

 and estimated to be three hundred and fifty feet in 

 thickness, and in some parts at least three times that 

 amount. These vast deposits are replete with these 

 little vegetable discs, usually converted into a highly 

 •bituminous, amber-like substance. 



Sporangites of similar microscopical character have 



been found, by Professor Huxley in the Better-bed 

 Coal of the Forest of Dean ; by Professor Newton in 

 the Tasmanian and Australian White Coal, and by 

 Mr. Orville Derby in the Erian strata of Brazil. In 

 Brazil the sporangites are often found still enclosed 

 in their original ovoid sporocarps in " every respect 

 resembling the sporocarps oi Salvinia uatansy 



Many other curious Rhizocarps are found in tho 

 Erian shales, some having affinities with Lycopods, 

 some with graceful fern-like fronds, others with bare 

 poverty-stricken looking stems (Psilophyton) with 

 rudimentary, or short and rigid leaves. 



"If," says Sir J. \V. Dawson, "we compare the 

 vegetation of these ancient plants (which played so 

 great a role in the Paleozoic world) with that of 

 modern Rhizocarps, we shall find that the latter still 

 present, though in a depauperated and diminished 

 form, some of the characteristics of their predecessors. 

 Some, like Pilularia, have simple linear leaves," resem- 

 bling Psilophyton ; others, like Marsilea, have leaves 

 in verticils, or whorls, and wedge-like in form, resem- 

 bling the graceful fossil Sphenophyllum ; while others, 

 like Marsilea, have frond-like leaves comparable to 

 the Erian Ptilophyton. 



{ To be continued.) 



THE MELBOURNE BOTANIC GARDENS. 



THE Melbourne Gardens lie about a mile from 

 the centre of the city, and when the splendid 

 bridge across the Yarra is finished, the approach to 

 Government House, the Observatory, and the Botanic 

 Gardens will be pleasant and convenient. The 

 gardens cover more than one hundred acres, reclaimed 

 from an absolute waste, and now rendered attractive 

 both scientifically and from the landscape gardener's 

 point of view. Due advantage has been taken of the 

 undulating character of the enclosure ; a few in- 

 digenous Eucalypti and other trees remain in statu 

 quo, lending an additional interest to the surroundings. 

 In one part especially, the retention of the original 

 conditions is particularly happy, harmonising with 

 the more recent additions of the gardener's art, yet 

 retaining the primitive wildness. The swampy ground 

 referred to lies low, dark peaty water with an islet 

 filling a hollow in a far extremity of the Gardens. 

 Clumps of she-oak {Casiiarina qtiadrivalvis) stand 

 here and there, with the Hakea and Banksia forming 

 the lower scrub. There is an air of wildness sugges- 

 tive of unoccupied lands ; as a matter of fact, the 

 spot has remained untouched since we first occupied 

 Port Phillip. The Casuarina has no affinity to the 

 oak ; the popular name is a corruption of native 

 words. At the first glance the tree might well be a 

 species of pine. A closer examination, however, 

 shows the dark green cylindrical spines to be jointed 

 in segments like an equisetum ; they might well 

 belong to a calamite of the coal-measures. In fact, 



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