Apkil 2, 1894.] 



KNOWLEDGE. 



98 



Fig. 8. — Eoot-hair with 

 trumpet-shaped widening. 



that the bacteroids are budded off from the hyphas, whereas 

 Prazmowski conjectures that they are formed from their 

 conteots inside them; this, however, is a mere supposition. 

 Prazmowslii states that he has not observed their develop- 

 ment directly, although he has taken the trouble to 

 cultivate them in very different nourishing media and 

 under the most variable conditions ; but this is not to be 

 wondered at when we consider that these organisms are 

 amongst the most minute in the vegetable kingdom. 



Experiments were after- 

 wards instituted (in 1888) by 

 Marshall Ward for the purpose 

 of determining what relation 

 existed between the tubercle - 

 forming organism of the bean 

 and pea respectively, and they 

 resulted in the conclusion that 

 they were one and the same. It 

 was also noticed that the young 

 root-hairs, with delicate cell- 

 walls, are especially liable to be attacked ; that at the place 

 of infection a brilliant spot makes its appearance, as pre- 

 viously stated. If this is not one of the bacteroids it is 

 difficult to say what it is. The resulting tube grows down 

 the cavity of the root-hair, developing at the expense of 

 the cell contents. 



In the lichens we have a fungus and an alga growing 

 together, the well-being of the fungus dependent on that 



of the alga, and 

 vu-e versa. The 

 fungal portion alone 

 produces the sexual 

 organs of the hchen; 

 the fimgus extracts 

 nourishment from 

 the substratum, 

 while the algal por- 

 tion decomposmg 

 the carbonic ajid 

 of the air provides 

 at least a large 

 amount of the car- 

 bon necessary for 

 the growth of the 

 compound organ- 

 ism. Two organisms 

 growing together in 

 this fashion are said 

 to live a symbiotic 

 existence. There 

 are many examples 

 of such partnerships 

 in the vegetable 

 kingdom, though sometimes the partnership is only helpful 

 to one of the symbionts, as in the case of all parasites. 



From researches conducted in 1888 and 1889, by Prof. 

 Marshall Ward, we have learnt more about the conditions 

 which rule the development of the tubercle and the 

 relations of the organisms to them. It was proved that 

 the relation between the organism and the host plant are 

 of the most intimate kind, and that the well-being of the 

 one depends upon that of the other. For instance, if the 

 growth of the plant were so modified that no more car- 

 bonaceous material was assimilated than it required for its 

 own development, then that of the tubercles was arrested, 

 and they were found to be very deficient in bacteroids. 

 In one experiment a stream of air was passed through the 

 water in which the plants were being cultivated. This 

 caused the plants to grow rapidly, but the amount of 



Fig. 9. — Magnified view of cells from 

 tubercle with branching hvpha;. 



carbon assimilation being disproportionate to their growth, 

 either no tubercles were formed or only very small 

 specimens made their appearance. 



It may be interesting to note a number of experiments 

 actually made in this connection by Prof. Marshall Ward 

 in 1889 :— 



" Six peas were placed in garden soil. 



" Six peas were placed in silver sand with cultural salts 

 including a nitrate. 



" Six peas were grown similarly in silver sand with 

 cultural salts but without a nitrate. 



" Six peas were placed in sand with traces of soil wash- 

 ings or with pieces of 

 tubercle added. 



" Six peas were 

 placed in sand steri- 

 lized by heating. 



" Six peas were 

 placed in sand to 

 which salts (includ- 

 ing a nitrate) were 

 added." 



On all the plants 

 grown, with the ex- 

 ception of those in 

 the sterilized media, 

 tubercles made their 



Fio. 10. — Section showing the widening 

 of the hypha on passing through cell- 

 wall. 



the plant and cultural medium is 



appearance. It was 

 also shown that if 



regarded as one system, there is a gain of nitrogen 

 either in the crop or in the medium surrounding the roots. 

 This nitrogen must have been taken from the ak. So far 

 as we know, the green plants themselves are unable to 

 effect such a gain, and we must conclude that its assimila- 

 tion was due to the tubercle-forming organism ; but where 

 does it get the energy to enable it to perform this operation ? 

 This seems to be derived from the protoplasm of the cells 

 of the green plant upon which it lives, and which it in 

 turn benefits by the nitrates assimilated. The precise 

 method in which the assimilation of the nitrogen of the 

 air is effected is still a mystery. When an element is 

 liberated owing to the decomposition of a compound, it is 

 said to be in a nascent condition. Now it is known that 

 hydrogen when in this state possesses especially powerful 

 properties, enabling it to effectunions with other elements, 

 or to decompose compounds which it could not under 

 ordinary circumstances attack ; and it has been recently 

 asserted by Windogradsky that in this condition hydrogen 

 unites with nitrogen in the living protoplasm of the 

 bacteroids. If so, the result would probably be the 

 formation of ammonia, which would unite with salts 

 derived from the soil, and thus the nitrogen would become 

 a source of food to the green symbiont. 



Prazmowski asserts that he has succeeded in cultivating 



the bacteroids 

 in nourishing 

 media, and that 

 they divide 

 indefinitely, 

 appearing as 

 minute motile 

 rods, and he ac- 

 cordingly places 

 them amongst 

 the Schizomy- 

 cetes or fission 

 fungi, the group 

 to which bacteria 

 belong. But it 



Fig. 



11. — Section 

 budding off 



showing bacteroids 

 from hrpheD. 



