44 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



their salts through it. Hence it was inferred that mycorrhiza was 

 especially necessary in forests where absorption and transpiration are 

 reduced. 



Neottia Nidus-avis, the bird's-nest orchis, has long attracted 

 attention. Prillieux * has described the rhizome and roots, showing 

 that each root can develop into a new rhizome having a bud at the 

 apex, and that the hypodermal cells are infested by the mycelium of a 

 fungus which was supposed to act symbiotically ; but later investigations 

 by M. Bernard t show that the hypha enters the undifferentiated embryo 

 by the suspensor end, and as the latter develops it begins to form a 

 tubercle, to "shut off" the fungus, so to say, producing much starch in 

 the zone beyond the line of infection. 



As the rhizome elongates the hypha penetrates every new root and 

 internode of the rhizome, the axillary buds being unable to develop until 

 " tuberisation " has become more vigorous and the floral shoot manages to 

 develop itself. 



This orchis, like numerous other infested plants, would seem to 

 finally consume the parasite (though Gallaud suggests the term " in- 

 ternal saprophyte "), for such it appears to be, inasmuch as brown 

 substances take the place of the " tangles " (Fr. peloton) of hyphae within 

 the cells. 



M. N. Bernard discovered that the tuberous roots of orchids are 

 always infested, the fungus entering the roots as soon as they penetrate 

 the soil, and tuberisation begins immediately afterwards. If the roots are 

 slow in developing, so is tuberisation. Hence it is inferred that infection 

 is a determining condition of tuberisation. 



Tracing the infection from the seed of Cypripediuin, it is found that 

 the fungus hypha enters by the suspensors and rapidly invades more than 

 half the oval, undifferentiated embryo. The epidermis is alone avoided. 

 As it advances and makes " tangles " in the cells a zone of cells is formed 

 above the infected part, the nuclei increase greatly in size, and starch is 

 formed. The hypha then consumes this starch as it enters the cells 

 progressively. After a time the hypha and its protoplasm are digested by 

 the host and destroyed, and the cell becomes dead. The healthy part of 

 the seed now continues to grow, so that the living portion of the fungus 

 becomes restricted to the basal part. At this stage an axial fibro- vascular 

 bundle is formed and an endogenous root appears above with absorbing 

 hairs. These parts are quite immune, and leaves then begin to arise. 

 The fungus, thus confined to the base of the embryonary tubercle, 

 vegetates, but grows no further, so that the stem and rhizome are entirely 

 destitute of the endophyte. 



Though the roots are at first quite free from the fungus they may 

 become infected from the soil, where the fungus is present. In the 

 struggle between the parasite and the cells, which it invades, the 

 adversary has finished by succumbing. 



The conclusion arrived at by M. Bernard is that " in an aseptic medium 

 the embryos (as of Cattleya) show signs of development ; but their 

 evolution is arrested at a very early stage. This period can only be passed 



* Ann. cles Sci. Nat. 4^ ser. v. 



t "Etudes sur la Tuberisation," Bev. Gdn. de Bot. xiv. 



