ORCHIDS 



ORCHIDS 



2387 



2643. 



Flower of Gramma- 

 tophyllum speciosum, 

 showing at the base of 

 a column a cuplike 

 depression to the an- 

 terior wall of which is 

 attached the labellum, 

 with a narrow claw. 



less woody, are not infected; and occasionally individ- 

 ual plants are found which appear to be free from the 

 fungus. In the roots of epiphytic orchids, also, the 

 distribution of the fungi is irregular, only scattered 

 islands of cortical tissue being as a rule infected. Only 

 the parts of the roots which are in 

 contact with the substratum con- 

 tain fungi. In forms like Vanda 

 and Vanilla, with superficial roots, 

 only the side of the root adjacent 

 to the substratum is infected, while 

 the other chlorophyl-bearing side 

 is free. 



Within the cells, the fungus has 

 the form of closely coiled and 

 interwoven masses of hyphse. ex- 

 cept in the root-hairs and in 

 the velamen, the spongy outside 

 covering of the roots of epiphytic 

 orchids, where long hyphse occur. 

 The endophytic mycelium is, as a 

 rule, connected with external 

 mycelium in the substratum by 

 means of hyphse passing through 

 the root-hairs, or, where these are 

 absent, as in Neottia Nidus-avis, 

 through the epidermal cells of the rhizome and the roots. 

 In some forms, like Neottia and the epiphytic orchids, 

 such communications have been only sparingly 

 observed, while Corallorhiza and most of the terrestrial 

 orchids have abundant connections with the mycelium 

 in the substratum. 



The plants are sometimes permanently infected 

 through the seedling in the way described farther on. 

 Infection also takes place 

 through the root-hairs. When 

 the rhizome and the upper 

 part of the roots are free 

 from fungi, infection must of 

 necessity take place in this 

 way. In epiphytic orchids, 

 and probably in terrestrial 

 orchids also, repeated infec- 

 tions thus occur. In some 

 terrestrial orchids, in which 

 the fungus invades the rhi- 

 zome, the hyphse grow out 

 directly from this into the 

 new roots, and also into the 

 bud for the following year. 

 In such forms only a single 

 infection is necessary to estab- 

 lish a permanent symbiosis. 



It is generally held that the mycorrhiza fungi supply 

 their hosts with nutrients. That the non-green forms 

 like corallorhiza are supplied with organic carbon com- 

 pounds in this way can scarcely be doubted, for these 

 plants, lacking chlorophyl, cannot elaborate their own 

 carbohydrates from the carbon dioxide of the air. It is 

 certain, also, as will be described later, that the germina- 

 tion of orchid seeds and the early stages of development 

 of the seedling do not take place without the interven- 

 tion of the mycorrhiza fungi, but the function of the 

 fungi in these processes re- 

 mains still to be investigated. 

 To what extent the mycor- 

 rhiza fungi function in sup- 

 plying the plants with water, 

 salts, and organic nitrogen- 

 ous compounds, is not known. 

 For the greater number of 

 orchids that are equipped 

 with chlorophyl and which 

 2645. Bulbophyllum Ach- therefore utilize the 



rochajne, showing (s, s) can > tfte j! 'P?' 

 lateral sepals decurrent on carbon dioxide of the air 

 foot of column. for the production of carbo- 



2644. Paphinia cristata, 

 showing at / the foot of the 

 column with labellum at- 

 tached on lower side. 



hydrates, it is not likely that the root-fungi are neces- 

 sary for supplying them with carbon compounds. There 

 is some evidence, however, that the fungi have a part 

 in supplying the plants with nitrogenous compounds 

 and possibly with phosphorus and potassium also. 

 The fact that the hyphal coils 

 are finally digested in the cells 

 and that the substances which 

 they contain thus become avail- 

 able to the plant, throws no 

 light on this problem for the 

 substances in the hyphse may 

 have been derived from the 

 plant itself. Investigations up 

 to the present time have shown 

 that orchids do not assimilate 

 free nitrogen from air by the 

 aid of their endophytic sym- 

 bionts, nor do the fungi them- 

 selves in pure cultures fix free 

 atmospheric nitrogen. 



Seedlings. 



The growing of orchid seed- 

 lings has always been sur- 

 rounded with much mystery 

 and secrecy. In the large 

 orchid establishments, the 

 secret methods which the ex- 

 pert growers were supposed to 

 Kssess were carefully protected 

 ' locked doors and painted glass, and visitors were 

 seldom admitted to the houses. Yet it was evident 

 that in spite of the carefully guarded practices, chance 

 seemed to play an important part in the culture of 

 orchid seedlings. Rarely were the expert growers uni- 

 formly successful. Of the vast number of genera 

 imported, only cattleyas, odontoglossums, cypripe- 

 diums and a few others could be grown with even a fair 

 assurance of regular success. Some growers were 

 unusually successful with one group and some with 

 another, but generally all were not equally successful 

 with all kinds. The key to this situation was furnished 

 by Noel Bernard who, in 1903, attempted to grow 

 seedlings of a hybrid between Cattleya Mossise and 

 Lsdia purpurata under aseptic conditions and found 

 that the embryos swelled and formed green spherules, 

 but that they failed to develop further even after weeks, 

 and finally died. If, however, the seeds were sown on 

 pure cultures of the endophytic fungus isolated from 

 the roots of these plants, the embryo developed nor- 

 mally, forming a spheriod body which soon produced a 

 cotyledon and papillae with 

 long root-hairs. Further 

 investigations, chiefly by 

 Bernard and by Burgeff , 



st 



2646. The mentum. 

 a, spur -like mentum of 

 Lycaste Cobbiana; b, 

 sack-like mentum of Acan- 

 thophippium javanicum; 

 c, chin -like mentum of 

 Batemannia Colleyi. 



2647. Cypripedium. st, 

 staminodium ; a, anther; 

 s, stigma. 



2648. 



Phragmopedilum caudatum. 

 st, staminodium; a, anther; 

 s, three-lobed stigma. 



showed that the germination of orchid seeds does not 

 occur except in the presence of the root fungi. Even 

 seedlings of such little mycotrophic forms as Cypri- 

 pedium and Epipactis, will not develop unless infected, 

 although the mature plants of these species are often 

 found without fungi and do not require their presence. 



