PHTSARUM. I PHYSAaACEiB. 51 



angles of the threads and with large lime-knots ; some may have erect 

 stalks enclosing much refuse, standing with others more weakly formed, 

 containing little refuse matter and cernuous from the weight of the 

 sporangium. As in all the Calcarineee. the amount of lime in the 

 sporangium-wall is liable to great variation ; where the supply is 

 abundant it gives firmness and persistence to the membrane ; where 

 it is scanty the wall is fragile or evanescent, as in the form named 

 Tilmadoche nutans. In contrast with the latter, a robust form occurs, 

 having a short stout stalk, often projecting within the sporangium in 

 a conical pcnnt, with lime-knots of large size, either distributed among 

 the capiUitium or confluent in the centre ; between these extreme 

 forms aU shades of difference may be found, making it difiBcuIt to 

 define even distinct varieties. Examination of a large series leads to 

 the conclusion that P. leucophceum is not a distinct species, but must 

 be included under P. nutans. The name P. leucophceuri has been so 

 long established as applied to a well-recognised form, that it would 

 have been desirable in some respects to retain it as representing the 

 type of this species ; but as the name P. nutans was given by Persoon 

 twenty-three years earlier than that by Fries, the rules of precedence 

 necessitate its adoption. 



The diverging forms may be approximately described as follows, 

 being arranged according to the amount of lime in the sporangium- 

 wall and oapillitium. 



a. violascens Rosfc., Men., p. 114; sporangium-wall iridescent, 

 fragile, free from lime ; capiUitium without lime-knots, stalk 

 cernuous. Spores nearly smooth, 8 to 9 /* diam. 



p. genuiuum : sporangium-wall with thin, innate clusters of 

 lime-granules, fragile ; capiUitium slender with few flat expansions 

 at the angles and few small lime-knots ; stalk cernuous. Spores 

 nearly smooth, 8 to 9 /i. diam. Tilmadoche nutans Rost., Mon., 

 p. 127. 



y. leucophseum : sporangium- wall with abundant lime, some- 

 what persistent, capiUitium with flat, often perforated expansions 

 at the axils, especially towards the base of the sporangium, lime- 

 knots many or few, fusiform or rounded, 5 to 20 /a diam. ; sessile 

 forms frequent ; stnlk erect or cernuous. Spores 8 to 10 /a diam. 

 P. leiicophceum Fr., Sym. Gast., p. 24. 



S. robustum : sporangium-wall with dense deposits of lime, 

 persistent. CapiUitium stouter, with wide flat expansions, lime- 

 knotg rounded or angular, 20 to 50 fj, broad, sometimes confined 

 to the centre of- the sporangium and confluent. Plasmodiocarp 

 forms frequent. Stalk short, erect, stout. Spores more dis- 

 tinctly warted, 9 to 1 1 /a diam. 



Plate XV.. A. — a. sporangia of form /3, x 20 ; b. capiUitium and spores, 

 X 280 ; c. spore, x 600 ; d and d'. sporangia of form between /3 and y, 

 X 20 ; «. oapillitium of d with abundant lime-knots, x 280 ; /. oapillitium 

 of d\ with few minute lime-knots, x 280 (England). 



B.— a. sporangia of form 7, x 20 ; J>. oapillitium and spores, x 280 ; e. 

 sporangia of form S, x 20 ; d. capiUitium and spores, x 280 ; e. spore, x 600 

 (England). 



The type of Til. gracilenta Rost., in the Strassburg collection, has 

 small, nearly globose sporangia of the form /3, and of a greyish-white 



