SYMBIOSIS. 147 



BACTERIAL SYMBIOSIS IN OTHER GREEN PLANTS. 



Hiltner evidently considers the root-swellings on Alnus as due to bacteria. He says 

 bacteria are present in the nodules and that there is a symbiosis, or at least that Alnus 

 glutinosa starves in nitrogen-free sand, or water, when they are absent and thrives in it 

 when they are present. We must await his promised full paper on this subject. Meanwhile 

 the reader is referred to his striking figure in Lafar's Handbuch der Technischen Mykologie, 

 Bd. 3 (p. 63), where also may be found references to the literature of the subject. Similar 

 claims are made for the Bleaginaceae, but the organism occurring in their root-nodules 

 is not specified by him in any other way than that it resembles the one in Alnus, but is 

 not the same. Very little is known respecting the nature of the root-nodules on Melampyrum 

 and other genera referred to by De Vries, Beyerinck, etc. They are good subjects for 

 further study. 



A common root-symbiosis in Orchidaceae, Ericaceae, Cupuliferae, Coniferae and some 

 other families is due to fungous filaments, the so-called Mycorrhiza, the literature of which 

 is now considerable. 



Some references to Alnus, etc., are given under Literature of Root-nodules of Legu- 

 minosae. Peklo says the growths are due to Actinomyces. 



Insectivorous Plants. 



In 1889, Tischutkin, stimulated apparently by Morren's first paper, attacked the 

 views of Charles Darwin and others respecting the insectivorous nature of Pinguicula, 

 ascribing the solution of the albumen, etc., placed on the leaves, to the presence of bacteria. 



He cultivated Pinguicula under bell jars. After stimulating the glands of the leaf 

 to secretion by laying dead flies on the surface, he replaced the flies by little cubes of cooked 

 egg albumen, and 18 to 22 hours later collected the leaves and put them into chemically 

 pure glycerin. A few days later the glycerin extract was filtered. It gave an acid reaction 

 as did the sap from the glands. He used this extract for seven series of experiments as 

 follows : 



In the first series he placed a piece of albumen and 2 cc. of distilled water in a test-tube. In 

 the second and third, 2 cc. of dilute hydrochloric acid (0.2 per cent and 0.02 per cent respectively), 

 replaced the distilled water. In the fourth, 5 drops of 0.2 hydrochloric acid were added to the 

 formtdaof No. i, and in the fifth, sixth, and seventh, 2 cc. of a soda solution (0.5 per cent, 0.25 per cent, 

 and 0.05 per cent respectively) , replaced the water in No. i . To each of these was added the glycerin 

 extract, beginning with 6 drops and gradually increasing it to 2 cc. In an eighth series gluten-fibrin 

 or gelatin was used instead of albumen. All experiments were made at room temperatures. In all 

 cases results were negative. There was no digestion of albumen or gelatin. The biuret reaction 

 showed that no peptone was present. On starch also the extract had no effect. 



As a control experiment, pieces of albumen were placed on the leaves and after 8 hours when 

 excretion of fluid had taken place, these were allowed to remain in it or were replaced by fresh pieces 

 of albumen, gelatin, or oxblood fibrin. Very small pieces of albumen were entirely dissolved, but 

 larger pieces, even after 42 hours, were dissolved only in part, the remaining part becoming pulpy. 

 The gelatin was always completely dissolved, small pieces in 24 hours, large ones after 40 to 42 hours. 

 This part of his observations corresponds fully to Darwin's. 



Considering it possible that some substance injurious to the ferment had been extracted by the 

 glycerin, Tischutkin repeated these experiments, using, instead of a glycerin extract, the sap col- 

 lected directly from the surface of the leaves by means of a capillary pipette. Part of this fluid was 

 left in glycerin 4 or 5 days, the rest was diluted with a small quantity of distilled water. Again the 

 result was negative. The addition of malic and formic acids did not alter the effect. Neither was 

 there any digestion at a higher temperature (32° to 35° C). For a control pure Russian pepsin was 

 used with positive results. 



Tischutkin thinks, therefore, that the solution of albumen on the leaves is due to some cause 

 other than the action of a ferment secreted by the gland-cells. He concludes that the plant merely 

 secretes a liquid favorable to the growth of bacteria, and that the bacteria produce the pepsin [trypsin] 

 which dissolves the albumen. 



