130 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



5. ISOTRIA Raf. 



1. Isotria verticillata (Willd.) Raf. 

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

 Sometimes confused with Mcdcola virginiana, which has a flocculent-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 woodB 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 ophioglossovks. 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. ARETHTTSA 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 viridijlora Reichenb.) 



10. IBIDIUM Salisb. Ladies'-tresses. 

 Flowers in several ranks. 



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



Lip oblong-ovate, white 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. Jong. 



-,,, , 3. I. odoratum. 



1< lowers in one rank. 



Leaves persistent, lanceolate 4 1 vernale. 



Leaves soon withering, ovate. 



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



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



1. Ibidium plantagineum (Raf.) House. 



Flats below Chain Bridge. May. Northern states, south to Va. {Spiranthes lucida 

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



2. Ibidium cernuum (L.) House. 



Wet meadows and margins of bogs. Sept. Eastern U. S. (Spiranthes ccrnua L. 

 Rich.; Gyrostachys ccrnua Kuntze.) 



