Nov. 1S97.] BOTANICAL SOCIETY OF EDINBURGH 75 



drops of the washings of such a soil, be added, the roots of 

 the plant are liable to develop uodules, and that liability 

 becomes a certainty if the unsterilised soil is one in which 

 similar plants well supplied with nodules have been 

 growing. The nodules make their appearance at a very 

 early stage in the plant's history usually, but it is not 

 unusual to find quite newly-formed nodules on the roots of 

 plants that are well advanced towards maturity. Modula- 

 tion may occur on the roots of almost any plants, and the 

 nodules may be due to a variety of causes. The nodules 

 here referred to are, however, of a special kind, and their 

 anatomy has been carefully studied. They are due to the 

 attack of a special organism. The generally accepted 

 view is that it is a bacterium, and that it enters the plant 

 by the hairs of the root. To discover the plan and mode 

 of attack, and the propagation of the organism through the 

 root tissue, is a matter of extreme difficulty, and it is not 

 to be wondered at that there is considerable diversity 

 of opinion regarding such matters. Frank, after much 

 research, thinks he has discovered the spot on the root 

 where a nodule will be formed, and around which will be 

 clustered a mass of bacteria, allured to the spot by some 

 inviting exudation emitted by the plant itself on purpose 

 to attract them. 



When the nodule has at length been formed, the changes 

 brought about in the tissues of the root are easily seen. 

 In a diagram of Frank's there is shown a microscopic 

 preparation where the nodule from the root of a pea is 

 permeated by what seems like the hypha of a fungus 

 that has gained entrance by a hair and forced its way 

 through the epidermis and cortical layer, and has caused 

 the formation of modified cells in the meristem. These 

 cells, under a high power, are found to be full of small 

 Y-shaped bodies, to which the name of bacteroids has 

 been given, and within the bacteroid are found very small 

 liighly refractive cocci, which are the bacteria which Frank 

 calls EMzohium Icguminosarum. 



In another diagram is shown a section of a nodule, 

 taken from tlie root of yellow lupine, in which the infection 

 has spread over a considerable part of the meristem, and it 

 is important to note how the cells have multiplied by 



