CHAPTER XXXV. 



PALAEOZOIC GYMNOSPERMOUS SEEDS. 



SEEDS are abundantly represented as fossils from Carboni- 

 ferous to Post-Tertiary deposits. The importance of fossil and 

 sub-fossil species in the later geological series has been demon- 

 strated by the investigations of Mr and Mrs Clement Keid and a 

 few other workers in this neglected field. In cases where it is 

 possible to assign seeds to their parent-plants the descriptions of 

 casts, impressions, or petrifactions are added to the account of 

 vegetative organs; but it frequently happens that seeds are 

 preserved only as detached specimens many of which have little 

 or no value as botanical records, while others that afford striking 

 examples of the possibilities of petrifaction as a means of preserving 

 the most delicate structures, are of great importance. In Volume 

 n. an account was given of such Palaeozoic seed-bearing organs 

 as Lepidocarpon and Miadesmia, and the genera Lagenostoma, 

 Sphaerostoma, and Trigonocarpus are dealt with in this volume 

 under Lyginopteris, Heterangium, and Medullosa. Certain seeds 

 afford some evidence as to the systematic position of the parent- 

 plants though insufficient to warrant more than a surmise as to 

 the nature of the vegetative organs: in several cases it is only 

 from the resemblance of detached seeds to types that on the 

 strength of more or less convincing evidence are referred to 

 definite parent-plants that any conclusions can be drawn with 

 regard to precise systematic position. In view of the occurrence 

 of several different types of seeds that retain their morphological 

 features, but cannot be assigned with any degree of certainty to 

 genera founded on vegetative organs, a special chapter is devoted 

 to a comparative study of selected examples with the object of 



