188 Transactions. 



invariably predominates. In most cases the bodies coming under the second 

 head will be found to be most numerous. 



An examination of the velamen tissue of these orchid-roots shows that 

 it almost invariably contains many colourless or brownish hyphae, which 

 l)ranch freely and wander through its cells, forming a loose network of 

 mycelial threads. The hyphae are septate, and it would sometimes appear 

 fTom their great variation in thickness that more than one species of fungus 

 was present. This is undoubtedly often the case. At maturity the velamen 

 is a dead tissue, and no coils of hyphae or yellowish masses such are seen in 

 the cortical cells are present in it. Where the hyphae are present in abund- 

 ance in the velamen that tissue is sometimes observed to be in a state of 

 decay ; indeed, in the older portions of some roots it has entirely dis- 

 appeared, and the exodermis is then the outermost layer. 



The passage-cells of the exodermis are often occupied by a scanty coil 

 of hyphae formed by threads which have entered from the velamen. Some- 

 times a mass of granular bodies occupies each of these cells, which, unlike 

 those of the velamen, contain living contents. Where extensive thickening 

 has taken place in the exodermal cells it is not always easy to demonstrate 

 the connection existing between the hyphae of the transfusion-cells and 

 those of the velamen, owing to the presence of a felty mass which often 

 Qfuards these cells on their outer sides. The transfusion-cells of the exo- 

 dermis are the ones which admit the fungal hyphae to the cortical tissues. 

 Having entered one of these passage-cells, a hypha usually forms a loose 

 coil, and then extends out into the cortex, where it may branch, and each 

 branch is generally seen to end in one of the yellowish masses above 

 described. Sometimes after forming a coil in one cell a "hypha enters an 

 adjacent cell, where it forms another coil, and it may do this in several 

 cells in succession. The hyphae which are found in the cortex are seldom 

 normal, and they generally present an unhealthy and impoverished appear- 

 ance. This ill-nourished condition is indicated by the presence of vacuoles, 

 and often by the collapse of the hyphal walls. The hyphae of the velamen 

 never have this unhealthy appearance. 



Where the roots of these orchids come into contact with hmnus, as they 

 usually do in the crevices of the bark of the supporting tree, or in the black- 

 material formed by the decay of lichens, mosses, &c., it is noticed that 

 jmmbers of hairs, much resembling the root-hairs of ordinary terrestrial 

 plants, are frequently developed. Sometimes among the other normal 

 hairs some will be seen which have become flattened, and then twisted in a 

 regular spiral fashion. The cavity of each hair usually contains one or more 

 fungal hyphae, which are continuous with those in the velamen. 



The foregoing description applies in all essential respects to both species 

 of Earina and to Dendrobium Gunninghamii, in which the velamen is usually 

 a well-marked tissue, and the roots of which are structurally very similar. 

 In the New Zealand species of BulhophyUmn and in Sarcochilus adversus 

 the velamen is poorly developed, being seldom more than two cells deep. 

 In Sarcochilus the hyphae of the velamen are very scanty, but 'the yellowish 

 masses in the cortical cells are often large and abundant. 



It is by no means easy to discover the exact physiological significance of 

 structures such as those briefly described, although such problems are of 

 supreme interest. It is well known that the roots of many plants growing 

 in soils rich in humus often live in intimate connection with the mycelia of 

 fungi inhabiting the soil. These associations are believed to be beneficial 

 to both organisms, and to such an alliance between the roots of one of the 



