NOTES AND ABSTEACTS. 



273 



become distorted and twisted as shown by Hiltner's figures. The root- 

 hairs die off on infected parts of the root, but remain on other parts. 

 The bacteria lie embedded in mucilaginous filaments, which have led 

 other observers to believe that the organism was a filamentous fungus. 

 The organism in Alder tubercles is nearly allied to that in Leguminosce, 

 and its action is otherwise very similar. The author's views on the 

 relationship of the organism and its host-plant in the Alder and Legu- 

 minosce are important. It is now generally accepted that the host- plant 

 aided by the root- tubercles can acquire nitrogen which is not available if 

 the tubercles are absent. Frank and others state that this results from 

 the absorption of the bacteroid bodies of the tubercle-organism by the host- 

 plant. Hiltner states that this is only the case when the organism is starved. 

 The normal and more frequent case (as proved by Nobbe and Hiltner's 

 researches) is that the host-plant, with the aid of ferments, absorbs 

 only portions of the bacteroids, and that the supply of nitrogen can 

 only continue if the organism can find ways and means to replace 

 absorption by the host. On the one hand, the tubercle-organism utilises 

 carbohydrates obtained from the host -plant ; on the other hand, nitrogen 

 obtained from the atmosphere. The bacteroids are regarded by Hiltner 

 as rudimentary sporangia, which give rise to chains of rod-like bacteria ; 

 the sporangia are evidence of a struggle on the part of the organism to 

 maintain itself. When the tubercle-organism is virulent, infection of 

 Leguminosce or Alder results in the formation of tubercles which do not 

 contain bacteroids ; the host-plant is not benefited, and may even be 

 injured if grown under conditions where nitrates are not obtainable from 

 the soil. 



The mycorhiza of Podocarpus consist of a filamentous fungus which 

 lives (as the figure shows) in the cortex of the roots. It is endotrophic, like 

 that of Neottia and other Orchids, and the mycorhiza are distinct from 

 the tubercle-growths or mycodomatia of Leguminosce, Alder, Elceagnns, 

 and Myricacece. The relation of host to fungus is that the former 

 partially absorbs the latter. The fungus obtains carbohydrates from the 

 host and nitrogen from the atmosphere. 



II. Prof. Tubeuf, about ten years ago, vigorously opposed the view of 

 Frank that forest trees obtained all their nutritive elements from the soil 

 through the activity of the ectotroph'c mycorhiza {i.e. modified roots 

 covered externally with fungus filaments). Tubeuf in this paper restates 

 his argument that forest trees have normal roots with root-hairs, which are 

 capable of supplying the plant with water and soil-salts ; mycorhiza may, 

 however, be developed under certain conditions. Stahl recently advanced 

 a theory that the presence of mycoihiza on plants facilitated the procuring 

 of water and soil-salts. This may be the case in plants with a small leaf- 

 surface (e.g. Heaths and Pines), or with leaves which do not give off 

 water easily (e.g. Oak) ; or it may occur in cases where water and salts 

 are difficult to obtain, either because the soil lacks them (as in sand), or 

 because of excessive competition by soil-fungi (as in peat, and forest 

 soils with much humus). Tubeuf, while admitting the general truth of 

 this theory, does not agree with all the details. Endotrophic mycorhiza 

 have only a limited communication with the surrounding soil, and 

 cannot, therefore, furnish water or salts to any great extent ; their 



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