1 903.] on the Origin of Seed-hearing Plants. 343 



direct clue to the origin of Spermophyta ; we must look elsewhere 

 for the key to our main problem. 



The vast number and variety of Fern- like remains throughout 

 the Palasozoic strata, wherever land-plants are known, is familiar to 

 all. Almost every form of recent Fern-frond can be matched from 

 the impressions in the Carboniferous and Devonian rocks. A con- 

 siderable number of these fossil Fern-fronds are known to have 

 really belonged to Ferns, for typical Fern-fructifications are found 

 upon them. 



An experienced collector of Coal-Measure plants, Mr. Hemingway, 

 once told me that he reckoned on finding about 20 per cent, of the 

 specimens of a true fossil Fern in the fertile state. When, therefore, 

 a common fossil Fem-frond (so-called) is never found fertile, a strong 

 suspicion is awakened that the plant must have had some kind of 

 fructification other than that of an ordinary Fern. This is the case 

 with a surprisingly large proportion of the Palaeozoic plants commonly 

 described as Ferns, and holds good of certain entire " genera " : the 

 important genera Alethopteris, Neuropteris, Mariopteris, Callipteris, 

 Tseniopteris, and others, have never yet been found, in any of their 

 species, with fertile fronds, if we except one or two specimens so 

 questionable and obscure that no conclusion can be drawn from 

 them. It is probably under the mark to say that one-third of the 

 so-called Ferns of Palaeozoic age aff'ord no evidence from fructifica- 

 tion that they were really Ferns, as we now define them. 



The absence of recognisable fertile fronds may, it is true, be 

 partly accounted for by dimorphism. Many Ferns, both recent and 

 fossil, bear their reproductive organs on modified portions of the 

 frond, or even on special fronds, very diff'erent from the vegetative 

 foliage. Fossil remains are usually fragmentary, and when the 

 sterile and fertile fronds are found isolated there may be nothing to 

 show that the one belonged to the other. But, allowing for this, 

 there are very many " Fern-fronds " which oifer no evidence, even 

 from association, of any Fern-like fructification, while the fructifica- 

 tions actually associated with them are often anything but Fern-like. 

 There are in fact a number of unassigned seeds from the Coal 

 Measures, some of which are commonly associated with certain of 

 the quasi-Ferns of which we are speaking. 



On the whole, however, we have, up to this point, had before us 

 merely negative evidence, indicating that many of the leaves, so 

 familiar to paleeobotanists, classed on account of their form and 

 veining as Fern-fronds, may really have belonged to some group 

 different from the true Ferns. Negative evidence is notoriously 

 weak; at most it only justifies us in taking up a position of philo- 

 sophic doubt, though in this case, it was enough to induce the 

 distinguished Austrian palaeobotanist Stur to suspect that the genera 

 Alethopteris, Neuropteris and others were no Ferns, but Cycads. 



During the last thirty years, however, positive evidence has been 

 accumulating, proving that certain of the Fern-like Palaeozoic plants 

 Vol. XVII. (No. 97.) 2 a 



