310 MYCORRH1ZAE AND MYCOTROPHY 



growth. She isolated the endophvte from several genera, getting 

 organisms that were morphologically similar but were dissimilar 

 in action when used reciprocally to inoculate seedlings. If, for 

 example, she inoculated seed of Phalaenopsis with the fungus iso- 

 lated from the same host, normal germination followed, and the 

 mycelium was kept in bounds by the digestive activity of the cells 

 of the embryo. If instead she used the fungus isolated from 

 Odontoglossum, germination stopped short at an early stage, and 

 intracellular digestion of the fungus was excessive. In certain 

 other orchids, such as Bletilla hyacinthia, the seed germinated even 

 when the fungus was absent, but the seedlings did not survive 

 beyond the first leaf stage. 



Bernard was able to grow seedlings to a size suitable for trans- 

 planting in the absence of the endophvte, if she supplied sugar 

 solutions and salep of varying concentrations. She interpreted 

 this ability to germinate in the absence of the endophvte to be 

 caused by a physico-chemical stimulus of the sugar and not to be 

 produced by the sugar as a food. 



More recently Knudson (1929) summarized a series of studies 

 (1922, 1925) on the food relationship in these non-symbiotic ger- 

 minations. He found that the embryos of Cymbidium, Vanda, 

 Ophrvs, and Epipactis lack chlorophyll for the first 5 or 6 weeks. 

 They must, therefore, obtain soluble food from the substratum in 

 which they are grown. When Knudson supplied Cattleya em- 

 bryos with sugar for the period of a month and then removed 

 them to a medium lacking sugar, the seedlings continued to make 

 good growth for 5 or more years. Sugar concentrations in pure 

 cultures as low as 0.02% yielded good (Terminations. Knudson 

 was also able, in PfefTer's solution fortified with a mixture of peat 

 and sphagnum and adjusted to pH 4.6, to germinate embryos just 

 as rapidly as occurs in the presence of the endophvte. .Moreover, 

 he was able successfully to substitute a species of Phytophthora 

 isolated from lilies for the true endophytic Rhizoctonia. He con- 

 cluded from these extensive studies that the unusual requirements 

 of orchid seed for germination must be explained by their inability 

 to synthesize food. The embryos must therefore be regarded as 

 saprotrophic in early development and the associated fungus as 

 mildly pathogenic, pathogenicity being controlled by the physio- 

 logical condition of the orchid. In criticism it may be noted that 

 the universal occurrence of the endophvte in orchid roots in 



