Oct. 13, 1881] 



NA rURE 



561 



sporangia are globose, pedunculated, and situated 

 towards the base of the bracts which compose the fruit- 



FiG. g. — Lepidostrobus the repr d ciive ort,an of Lepidodendron. Longi- 

 tudinal section of sporang ocirp of Z«/; iosttobus Diladianns, Schimp., 

 showing the I wer p ring a containing macrospores and the upper 

 microspores half natural bize 



splices, and either contain two to eight macrospores, or 

 small and ^'ery numerous microspores. In the germina- 



tion of these spores the approach towards Gymnosperms 

 becomes exceedingly apparent, and is consequently dwelt 

 on at some length, the researches of Sachs, Luersen, and 

 others being largely referred to. An even higher stage 

 was in all probability reached in the Lepidodendrons, the 

 vigorous and splendid growth of which formed the cul- 

 minating development of the Lycopodiaceoe. The mathe- 

 matical regularity of their growth, even in the moEt 

 minute internal structure, is ver)- striking. They formed 

 large trees with acicular or falcate, perhaps deciduous 

 leaves, and bore cones in pairs at the extremities of 

 certain branches, differing exteriorily but little from those 

 of Gymnosperms. The expanded bases of the scales or 

 bracts bore the sporangia, those containing the macro- 

 spores being nearest the base. The stem comprised 

 several layers, the centre being of pith formed of elon- 

 gated prismatic cells. The next layer was woody, and 

 gave off simple vascular threads to each leaflet, these 

 penetrating obliquely the succeeding region of paren- 

 chyma and the cortical layers. The bark increases in 

 density towards the exterior, and in some species the 

 interior pith is absorbed in the woody layer. 



Lepidodendron, with the greater part of the Paleozoic 

 flora, became extinct during the Permian, leaving as re- 

 presentative the humble Isoetes. This, however, is not 

 necessarily a degraded type, and may have existed since 

 Pateozoic times, though only known fossil in the later 

 Eocenes, where it in no way differs from existing forms. 



The Rhizocai-ps are beyond doubt the highest existing 

 form of Cryptogam, but though in many respects so nearly 

 approaching to Phanerogams, they are not, as we see 

 them now, in the absolutely direct line of evolution. In 

 all, the sporangia are protected by an enveloping altered 

 leaf, or segment of a leaf, forming a fruit called a sporocarp, 

 which in most cases attains a high degree of complexity. 

 The entire group is aquatic, and stands in the same 

 position towards fossil Rhizocarps that Isoetes does to 

 the Lepidodendrons. The Carboniferous Sphenophyllum 

 has been shown to correspond to Salvinia, and the Rhsetic 







IS 



i/jid 



#, \H ^^'^^ 



y/jis 



10.— Rcpr. ductive organs of Lepidodendrcn with microsporangia and microspores. A, longitudinal section through upper part of sporangiocarp 

 of Lep:d strobus (probably L. Broivnii, Schiinp ), from the neighbourhood of Pe'zcnas (Herauli) : M, the central medullary region formed of 

 parenchyma with elongated prismatic fells : v v, (he woody layer of fibro-vascular region next the pith, showing large scalariform vessels ; L, 

 lacuna, in which delicite and partly disintegrated cells are studded; cc, cortical layer composed cf a very dense outer and an inner layer, 

 separated by a loose, nearly destroyed parenchyma; s, " sporangiospores," supporting very eh ngated micro.-porangia filled. MS, with 

 microspores aggregated in fours (these are slightly exaggerated in size) ; B, group of microspores magnified. 



Sagenopteris to the Marsiliacese. Though the vegetative 

 organs in the extinct forms attained far tiner proportions 

 and a higher and more delicate structure, the fructitica- 

 tion, in Salvinia especially, appears the more complex. 

 The existing genera have only been met with in the 

 Eocene and Oligocene. 



Thus while Angiosperms all present similarity in the 

 reproductive process, Cryptogams preserve many of the 



stages by which the evolution of the higher forms has 

 been accomplished. They also present every gradation 

 in their vegetative organs, from the simplest and purely 

 cellular plant to the equals of Phanerogains in point of 

 structure. Except the Protophytes, all Cryptogams are 

 impregnated by antherids, and present the antagonistic 

 and alternate asexual and sexual generations, these being 

 in fact their distinguishing characters. The authors' task 



