﻿GATES— PAIRS OF SPECIES 



less supplemented by histological or experimental investigations, 

 may lead to quite erroneous ideas concerning the relationships of the 

 species within a genus. There needs to be developed a taxonomy 

 based upon the anatomical and cytological structure of plants, as 

 well as upon the traditional comparison of their external morphology. 

 This need has often been emphasized, and it appears now to be 

 time to begin to put the principle into practice. If the present paper 

 leads to the closer scrutiny of known species from this aspect its 

 purpose will have been accomplished. 



An instructive example of the value of cytology in determining 

 relationships has recently been furnished by Spiranthes (Gyrostachys) 

 cernua (L.) Richard. Reasoning by analogy from the case of 

 Oenothera gigas, Miss Pace 1 found that it is a true cell giant, having 

 twice as many chromosomes as S. gracilis (Bigel.) Beck, and a cor- 

 responding increase in cell size and stature. The two species are 

 shown in fig. i. S. cernua is conspicuously larger in all its parts, 

 having larger flowers, stouter stems, and longer, though usually 

 narrower, leaves. 10 There is variation particularly in the length of 

 the spike and the width and shape of the basal leaves. 



Andrews 2 observed three distinguishable forms of S. cernua 

 in a meadow at Williamstown, Massachusetts. The type is pure 

 white and fragrant. A variety which was the common form in 

 this meadow differed in having cream colored or yellow flowers 

 which were not fragrant, a shorter, broader, and more rounded 

 or 2-lobed lip, and leaves also distinct in shape and structure. A 

 second variety, found in one spot some distance away, was white 

 flowered, but otherwise agreed with the yellow variety. Similar 

 forms are recorded from Manchester, New Hampshire, and from 

 Mount Desert Island, Maine. A var. ochroleuca (Rydb.) Ames 

 has also been described, having greenish, cream colored or white 

 flowers, longer floral bracts, growing in dry ground, and blooming 

 somewhat later. The tetraploid S. cernua would thus appear 



1 In S. gracilis 21-30, while in S. cernua 2.v = 6o. Tack, Lula, Two species of 

 Gyrostachys. Baylor Univ. Bull. 17. no. 1. pp. 16. figs. 50. 1914. 



* Figures of these species are also found in Torrey, Fl. N.Y. 2: 282. pi. 129. 



ill. 1899. ' LERC *' ° n S ° me %anatlonsof S P' ra " lhcs cer " ua - Rhodo a 1. 1 10- 



