1921] Ames, — Notes on New England Orehids, — I. Spiranthes 77 



Beckii Lindl. are provided with roots that at flowering time are free 

 from mycorrhizal fungi except for a small area at the base of the stem. 

 Cross sections of the roots at any point a few millimeters below the 

 base of the stem will be found simply filled with an abundance of 

 food material. This accounts, perhaps, for the failure of at least 

 one observer to find fungal hyphae in the root of S. Beckii .' In the 

 study of the roots of Spiranthes in connection with mycorrhiza it is 

 best to make longitudinal sections, as cross sections are likely to be 

 inconclusive. From a study of these longitudinal sections it would 

 seem that certain areas of the root have the capacity to repel the ad- 

 vance of the fungus and that in this respect the roots of Spiranthes 

 are comparable to the bulbous thickenings of certain species of the 

 Ophrydeae studied by Noel Bernard. 2 It is as if there were some 



Figs 1-4. Throe stages of development in the seedlings of Spiranthes ccrnua. 

 1. Protocorm and two leaves before the formation of the first root ( X3). 2. A 

 mere advanced stage before formation of a root ( X2). 3. A young plant with 

 the protocorm still present and the first root developing (XlMK All as found 

 in September growing within a few inches of each ether and apparently seedlings 

 of equal size. 4. Seed of Spiranthes cernua var. ochroleuca (highly magnified). 



fungicidal capacity in the cells of the root-structure that restricts 

 the fungus to a limited area. Or, we may have, in the case of Spir- 

 anthes, an example of those plants that are able to defend them- 

 selves against an intrusive fungus by means of a digestive process 

 that protects tissues of vital importance. In other words, there are 

 two types of cells in the root-system, one type characterized by a 

 capacity to digest the fungus and hold it in check, the other type, 

 found in infected regions, characterized by the capacity to act sym- 

 biotically with the invading fungus. 



« T. Holm, Am. Journ. Sci. xviii (1904) 205. 



2 Annates des Sciences Xaturelles Botanique, xiv (1911) 222-234. 



