[Vol. 2 



702 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



plant with a substipitate base, an incurved margin, and short 

 tubes. One figure shows the plant from a front-underneath 

 view, the other shows half of the plant with the cut surface 

 outward and the hymenium upward. Plate 212 shows prac- 

 tically the same thing but with a little more detail, and it is a 

 fair representation of P. betulinus. All later descriptions of 



P. 



based 



on 



plants that have no resemblance to the one that has since been 

 referred to P. spumeus. Fries' description 1 says: "basi 

 stipitif ormi, margine incurvato. ' ' 



This gives us but two alternatives from which to choose. 

 Either Sowerby confused his illustrations of P. spumeus and 

 P. betulinus and inserted two plates of the same species (P. 

 betulinus), or else there existed at that time a plant closely 

 related to P. betulinus but growing on elm and thought by 

 Sowerby to be distinct. Since the mutual resemblance of 

 Sowerby 's two plates is so great, it is the writer's opinion 

 that he had drawn two plates of P. betulinus and by mistake 

 inserted both of them instead of one of that species and one 

 of P. spumeus. This theory is borne out by the fact that he 

 makes no mention of a stipe-like base nor an incurved margin 

 to the plant. We may also conclude that Fries' description 

 was drawn, in part at least, from pi. 211, for it is incon- 

 ceivable that with access to Sowerby 's figure he would have 

 referred to that species a plant that departs so widely from 

 the authentic illustration, unless he was also of the opinion 

 that pi. 211 was a mistake. 



This mistake (for so it seems we must regard it) has caused 

 some little confusion in the literature. Fries' idea of P. 

 spumeus was evidently gained, in part at least, from Sower- 

 by 's plate, for he refers as a synonym for P. spumeus, Boletus 

 suberosus of Wahlenberg 2 . But Wahlenberg was aware of 

 the existence of a Boletus suberosus of Linnaeus 3 and ex- 

 pressed the doubt that his species was the same as that one. 

 Boletus suberosus of Linnaeus has always been regarded as 



1 Hym. Eur. p. 552. 1874. 



2 Fl. Upsal. p. 457. 1820. 

 3 Sp. Plant, p. 117G. 1753. 



