280 PTERIDOPHYTA. [CH. 



examples of tubers as this Wealden plant. By some of the 

 earlier writers the detached tubers of E. Burchardti were 

 described as fossil seeds under the name Carpolithus. 



Fig. 66. Equisetites Yokoyamae Sew. From specimens in the British 

 Museum. Nat. size. 



The specimens shown in fig. 66 have been referred to 

 another species, E. Yokoyamae Sew.*; they were obtained from 

 the Wealden beds of Sussex, but according to Mr Rufford, 

 who discovered them, the smaller tubers of this species are not 

 foimd in association with those of E. Burchardti. The stems 

 are very narrow and the tubers have a characteristic elliptical 

 form; the species is of little value botanically, but it affords 

 another instance of the common occurrence of these tuberous 

 branches in the Wealden Equisetums. 



Similar fossil tubers, on a much larger scale, have been 

 found in association with the Triassic Equisetites arenaceus; 

 with E. Parlatori Heer^ a Tertiary species from Switzerland, 

 and with other Mesozoic and Tertiary stems. E. Burejensis^, 

 described by Heer from the Jurassic rocks of Siberia, bears a 

 close resemblance to the Wealden species. 



The description of the above species by no means exhausts 

 the material which is available towards a history of fossil 



Seward (942) p. 33. ^ Heer (55) vol. iii. p. 158, PI. cxlv. 



Heer (77) p. 99, PI. xxii. 



