130 CONTRIBUTIONS PROM THE NATIONAL. HERBARIUM. 



6. ISOTRIA Raf. 



1. Isotria verticillata (Willd.) Raf. 



Low rich woods. May-June. Eastern U. S. {Pogonia verticillata 'Nutt.) 

 Sometimes confused with Medeola virginiana, which has a floeculent-woolly green 



stem, while Isotria has a glabrous purple stem. This species has the reputation of 



disappearing from its usual haunts for several years in succession and then reappearing. 



Its coloring is very highly protective. 



6. TRIPHORA Nutt. 



1. Triphora trianthophora (Swartz) Rydb. 



Low rich woods along the Potomac. Eastern U. S. {Pogonia trianthophora B. S. P.; 

 P. pcndula Lindl.) 



While possibly not our rarest orchid, this little plant is certainly the hardest to find. 



7. LIMODORUM L. 



1. Limodorum tuberosum L. Grass-pink. 



Bogs; usually associated with Pogonia ophioglossoides. Eastern U. S. {Calopogon 

 pulchellus R. Br.) 



Pale, nearly white forms are occasionally found. Strikingly peculiar in having the 

 lip erect, while all our other orchids have pendent lips. 



8. ARETHirSA L. 



1. Arethusa bulbosa L. Arethusa.- 



Gravel bogs near Suitland and Hyattsville; rare. May. Eastern N. Amer. 



9. SERAPIAS L. 



1. Serapias helleborine L. 



Our only introduced orchid, well established in the Soldier's Home woods, probably 

 persisting from the planting around some old homestead. July. Native of Europe. 

 {Epipactis viridiflora Reich enb.) 



10. IBIDIUM SaUsb. Ladies'-tresses. 



Flowers in several ranks. 



Lip quadrate, yellowish; lower leaves oblong-lanceolate 1. I. piantagineum. 



Lip oblong-ovate, wliite or greenish white; leaves all narrowly lanceolate. 

 Flowers only slightly fragrant, apparently arranged in four vertical rows; bracts 



curved, shorter than the flowers; plants not stoloniferous 2. I. cernum. 



Flowers decidedly fragrant, in evident spiral rows; bracts erect, equaling or 

 exceeding the flowers; plants producing stolons sometimes 10 cm. long. 



3. I. odoratum. 

 Flowers in one rank. 



Leaves persistent, lanceolate 4. I. veruale. 



Leaves soon withering, ovate. 



Roots fascicled ; lip green, with wliite margin; flowering in July 5. I. gracile. 



Root usually solitary; lip all white; flowering in September 6. I. beckii. 



1. Ibidium piantagineum (Raf.) House. 



Flats below (^hain Bridge. May. Northern states, south to Va. {Spiranthcs lucida 

 Ames; S. latifolia Torr.; Gyrostachys plantaginea Britton.) 



2. Ibidium cernuum (L.) House. 



Wet meadows and margins of bogs. Sept. Eastern U. S. {Spiranthes cemua L. 

 Rich.; Gyrostachys ccrnua Kuntze.) 



