FUNCTION OF MYCORRHIZAE 



309 



tion of the nature of endotrophic mycorrhizae. In an earlv re- 

 port * she concluded that the fungal component is a benign para- 

 site causing chronic pathogenesis. She became interested in this 

 problem because of the difficulty that orchid growers were experi- 

 encing in germinating seed and raising seedlings. In the green- 



Fig. 49. A. Short, lateral roots dichotomously branched, typical of mycor- 

 rhizae on pine. B. Somewhat enlarged mycorrhizae on pine. (After 

 Hatch.) C. Sketch of ectotrophic mycorrhiza on pine, showing mantle 

 and "Hartig net." (After Doak.) D. Locus of endotrophic mycorrhiza 

 (stippled area) in germinating orchid seed, Odontoglossum. E. Cell from 

 stippled area showing hvphae of Rhizoctoma lanuginosa. (After Bernard.) 

 F. Ectendotrophic mycorrhiza in cell of strawberry root. (After O'Brien 



and McNaughton.) 



houses of successful growers she noted that certain fungi were 

 present in the soil around the roots and that endotrophic mycelium 

 occurred within the tissues. If seed were sown near parent plants, 

 germination resulted. If the seed were grown aseptically, ger- 

 mination failed. These observations led her to believe that the 

 presence of the endophvte was essential for germination and 



* She considered orchids, ''comme les plantes atteintes d'une maladie 

 parasitaire chronique qui commence a la germination et persiste en general 

 jusqu'a l'etat adulte; maladie benigne en un certain sens. . . ." 



