303 



In other words, Hellriegel believes that these little bodies are 

 really bacteria, and that they have the power to make use of the 

 nitrogen, that they work it over into a form which the plant can 

 use, and it is appropriated by these tuber-producing plants. 



On the other hand, Frank holds that the experiments of 

 Hellriegel do not bear out this conclusion, that the ability of 

 plants to assimilate free nitrosjen is much more extended than the 



o 



experiments of Hellriegel lead us to suppose. He has nowhere 

 given so clear and succinct a statement of his conclusions as Hell- 

 riegel, but he claims that the fact of the Leguminosse producing 

 more nitrogen than any other plants proves nothing in reference 

 to their need of any special organ for this purpose. He lays 

 much stress on the fact that at certain periods of their life they do 

 not assimilate more nitrogen than other plants; for example, be- 

 fore blossoming they assimilate much slower than after that time 

 up to the ripening of their fruit. This he gives as a possible solu- 

 tion of the Boussingault experiments, namely, that they were 

 made at such a time in the development of the plants when they 

 were not using much nitrogen. Again he argues: it is admitted 

 that some plants have a greater power of assimilating CO^ than 

 others; why not also a difference in regard to nitrogen? Furth- 

 ermore, he claims to have proven that plants belonging to other 

 families than the Leguminosse, as certain Crucifera^, Gramineae 

 and some Algae, in none of which these tubers occur, have yet 

 the power to use free nitrogen of the air. He says that it has not 

 been proven that these bacteroidea are able to assimilate nitrogen, 

 but that this is known to be the part of the green plant. 



Frank appears opposed to nearly all the botanists now at 

 work at this question and those involved in it, in these two par- 

 ticulars. He holds that more plants assimilate free nitrogen than 

 those having these peculiar tubers and belonging to the family 

 Leguminosa^, and also that these httle bodies, discoved by Wor- 

 onin, are the normal product of the plant, and have no connec- 

 tion whatever with any outside organism. 



Now the next step in this interesting question follows very 

 naturally. This is: Do bacteria act in the process of changing the 

 ammonia of the air into nitrates? This question, like many oth- 

 er physiological ones, has long been the study of chemists. Once 



