210 BOTANY 



thaceae, Ekinanthus, Euphrasia, and Pedicularis, may be mentioned as 

 examples of plants showing these peculiar conditions. Another 

 member of the same natural order, Melampyrum, has, on the other 

 hand, developed a saprophytic mode of life. The Mistletoe (Viscum 

 album), although strictly parasitic, possesses, nevertheless, like many 

 of the allied foreign genera of the Loranthaceae, fairly large leaves 

 well supplied with chlorophyll, and fully able to provide all the 

 carbohydrates required. 



Humus plants, like some of the Orchidaceae (Neottia, Coralliorrhiza, 

 etc.), and the Monotropeae, are restricted to a purely saprophytic mode 

 of nutrition, and to that end utilise the leaf-mould accumulated 

 under trees. The thick roots or rhizomes of these plants offer so 

 little surface for the absorption of nourishment, that it appears as if 

 the threads of the Fungi, which are always found knotted and coiled 

 together in their outer cells, and the free ends of which spread out in 

 surrounding humus, must in some way co-operate in their nutritive 

 processes. 



The roots of green plants which live in a soil rich in decaying vegetable matter 

 possess similar fungoid growths which, as in the above-mentioned Orchids, lie 

 partly rolled up in the root-cells, and in part spread out in the humus. Interwoven 

 masses of hyphse sometimes so thickly surround and encircle the young root-tips 

 that a direct absorption by the roots from the soil is rendered impossible. These 

 give rise to a formation known as Mycorkhiza. In this manner, according to 

 Fbank, the root-tips of the forest-forming Oupuliferae and Coniferae, as also of 

 many Ericaceae, are always covered by a fungus sheath. This fungus vegetation 

 appears to be in no way injurious, but, on the contrary, probably of benefit, at least, 

 judging from the results of culture experiments made with these plants without 

 mycorrhiza. As yet, the mutual relations existing between the Fungi and the 

 flowering plants is not fully understood ; possibly their connection may be a sym- 

 biotic one, in which the fungus hyphse perform for the trees the functions of the 

 root-hairs, and, in turn, receive from the tree a part of their nourishment. 



A marvellous relation between roots and Bacteria exists in the case 

 of the Leguminosae. It has long been known that peculiar outgrowths, 

 the so-called root-tubercles, are found on the roots of many Legu- 

 minosae (Bean, Pea, Lupine, Clover, etc.) (Fig. 186). Within the 

 last few years, the astonishing discovery, has been made that these 

 tubercles are caused by certain Bacteria, chiefly by Rhizobium legumi- 

 nosarwm (Bacillus radicicola). These Bacteria penetrate through the 

 root-hairs into the cortex of the roots, and there give rise to the tuber- 

 cular growths. These tubercles become filled with a bacterial mass, 

 consisting principally of swollen and abnormally developed (hypertro- 

 phied) Bacterioids, but in part also of Bacteria which have remained 

 in their normal condition. The former seem to be eventually consumed 

 by the host-plant, while the latter remain with the dead roots in the soil, 

 to provide for future reproduction. As the experiments of Hellriegel 

 and the investigations of Nobbe, Beyerinck, and Frank prove, 



