56o 



NATURE 



{Oct. 13, 1881 



increasing differentiation in tiie organ, or its support, can 

 be traced— one leading to the Polypodiaceas through 

 the Cyathcc-e, the other to Schizeaces, Gleicheniacew, 

 and Marat tiacete. 



The earliest fern of which the fructification is known is 

 the Devonian Palasopteris, Schimper. Its fructification 

 consists of aborted leaflets supporting groups of oblong, 

 ringless sporangia opening into two valves and disposed 

 in threes on pedicles. Rhacopteris, of the same age, and 

 perhaps not generically differing, has fructification which 

 unites in a higher degree the characteristics of Osmunda 

 and Botrydium, and giving birth probably to the lio- 

 tryopterideJE of the later Carboniferous flora. Another 

 genus, Seftenbergia, is allied by the structure of its 

 sporangium to Angiopteris (Marattiacea;), though each 

 sporangium is as yet isolated. The Paleozoic ferns did 

 not at this period essentially difter from Osmunda and 

 Todea. 



The earliest example of definite grouping in the 



Rha?tic. They seem to have developed suddenly, and 

 among them are a number with their sporangia grouped 

 in sori as in Gleichenia, yet possessing in other respects 

 the structure characteristic of Polypodium. 



The CiphioglossaccM are related to the most ancient 

 ferns by the arrangement and structure of their sporangia, 

 and to Isoetes and Lycopods by the form of their pro- 

 thalius. They even present affinities with Sigillaria, and 

 represent, the authors conjecture, an almost unchanged 

 type, older than the differentiation of either ferns, Lyco- 

 pods, or Rhizocarps. 



The Lycopodiace^e are divided into isosporous and 



Fig. 7.— I, magnified pinnule of one of the Lyg'-diea; :.f the genus Mohria. 

 showing the arrangement of the sporangia on the underside of the 

 frond; 2. sporangium of the same, showing the group of apical cellules 

 which disrupt the spore-case; 3. sorus of Gleichenia, showing the 

 peripheral arrangement of the cellules which disrupt the spore case ; 4, 

 sporangium bef jre dehiscence. 



sporangia is furnished by Oliogocarpia, in which three to 

 five sporangia are inserted on a point near the ultimate 

 terminations of the venules ; but even here, though con- 

 tiguous, they are distinct, and can be separated. In the 

 later Carboniferous, Marattioid ferns for the first time 

 occur with the sporangia united in a composite organ 

 called a synangium, and soon after the Marattiacea; 

 reached their maximum development, and commenced, 

 through forms now extinct, to difterentiate towards the 

 Gleicheniaces. The slaves of development of the latter, 

 and of the Schizeacea;, are more difficult to trace, though 

 both are represented in the Palsozoics by Howlea and 

 Seftenbergia respectively. The actual genus Gleichenia 

 does not appear until the inferior O'olite, and Lygodium 

 until the Cretaceous. 



Ttie Cyathese are represented in the Carboniferous by 

 Thyrsopteris and in the Jurassic by Dicksonia, while true 

 Polypodiese crinnot be traced farther back than the 



Fig 8. — I. part of pinnule of Angiopteris, with sporangia clustered in 

 groups, hut not united ; 2. part of pinnule of Marattia wiih sporangia 

 joiu'jJ together in a synangium; 2rt, a synangium magnified; 3, 

 exLiemi y of the fertile frond of one of the Cyatheas, Thyrsopteris 

 elt-giTns : 4, a majnified ri^ceptacleof the same, m form of a pedunculated 

 cup. full of sporangia which are girt w.th a jointed ring of cellules ; 

 5, section through an empty cup. sh wing the support to which 

 the sporangia are attached; 6, twj highly-magnified sporangia of 

 Pulyp .diaceje, one dehiscent, girt vertically by a j.jinted ring and on 

 pedicles. 



heterosporous kinds. The former, comprising Lycopo- 

 diuni and a few tropical genera, have been found fossil in 

 the Old Red of Thurso and the Carboniferous of Saar- 

 bruck and Autun, their small size and retiring habits 

 having doubtless caused their relative rarity in stratified 

 rocks. The heterosporous, or more perfected kinds, ob- 

 tained a magnificent development in the Carboniferous, 

 favoured by the warm and humid climate, free from 

 seasonal changes, which then seems to have prevailed, 

 and only declined when these conditions ceased. They 

 are at present represented by SelagincUa, a genus which 

 has scarcely changed since the Carboniferous. The 



