xxx. Stipe snow-white, fragile 37. _P. leucopus_

xxxx. Stipe generally distinctly fluted

+ Sporangia laterally
compressed, fan-shaped 38. _P. compressum_

++ Sporangia typically
globose, umbilicate
below, connate, etc.,
strongly calcareous 39. _P. notabile_

+++ Sporangia reniform,
concave below _P. affine_,
see under 38

++++ Sporangia larger, to 1 mm.,
nearly limeless,
iridescent 40. _P. tropicale_

oooo Sporangia obovate, compound,
clustered, the stipe fuscous,
fluted, short. 41. _P. nicaraguense_

OOOO Sporangia yellow, rarely iridescent or brown.

o Capillitial nodes white.

x. Stipe also white 42. _P. sulphureum_

xx. Stipe flesh-colored,
spores smaller 43. _P. carneum_

xxx. Stipe red or reddish brown 44. _P. citrinellum_

xxxx. Stipe yellowish, flaccid,
sporangia leocarpine 45. _P. albescens_

xxxxx. Stipe very short or none,
sporangia cylindric, brown 46. _P. variabile_

oo Capillitium nodes yellow or orange-yellow.

x. Badhamioid,
larger,--to .8 mm. 47. _P. auriscalpium_

xx. Physaroid, base persistent 48. _P. oblatum_

ooo Capillitium nodes pure yellow.

x. Capillitial threads yellow 49. _P. galbeum_

xx. Capillitial threads hyaline 50. _P. tenerum_

xxx. Peridium iridescent.

+ Capillitium persistent 51. _P. flavicomum_

++ Capillitium less
persistent, larger 52. _P. bethelii_

SECTION II. TILMADOCHE

I. Aethalioid, gyrose or irregular 53. _P. gyrosum_

II. Fructification stipitate.

1.