BOT.-VOL. II.] PEIRCE-ROOT-TUBERCLES. ZO\ 



It would appear from another experiment that not all con- 

 tacts and infections of root-hairs with tubercle bacteria lead 

 to the formation of tubercles. Among the seedlings grow- 

 ing in sterihzed moist chambers, I infected some with 

 bacteria from a gelatine culture of Bur Clover tubercle 

 bacteria. The next day showed a great increase in the 

 number of bacteria, but the tips of the root-hairs, though 

 bent in many instances, were not coiled in the manner usual 

 in infections, but instead, were cut off into short sausage- 

 shaped, often non-nucleated segments. In this way the 

 bacteria which have entered a root-hair are excluded from 

 the more vital parts of the root, just as gonidial cells in 

 lichens are known to exclude the haustoria of the fungus 

 by so dividing that only one daughter-cell contains any part 

 of the haustorium which has penetrated the mother-cell 

 (Hedlund, 1892; Peirce, 1899). Once given the contact 

 with the bacteria, the root-hairs can become infected; but 

 these infections may be resisted by the leguminous plant by 

 cutting off the infected parts. 



I am by no means ready to attach especial weight to the 

 result of this experiment for the following reasons: First, 

 I did not repeat the experiment, important though it would 

 be to prove that the root-hairs do cut off the infected por- 

 tions; second, this result followed the infection of the 

 sterile root of a seedling, not by bacteria suspended in 

 water but by stroking the root with a platinum needle which 

 had been dipped into a culture of the bacteria. By this 

 means not only bacteria but also their accumulated pro- 

 ducts in the culture-medium were put upon the root. It 

 might well be that these products, rather than the bacteria 

 themselves, so irritated the root-hairs that they segmented 

 as above described. It would be interesting to follow this 

 matter to a decisive conclusion, but it was not possible at 

 the time to do so, and this point was not directly connected 

 with the main object of this investigation. It may be that 

 by similar means the root-hairs, and thereby the roots, of 

 other than leguminous plants resist and escape infection 

 by the bacteria which so characteristically affect the 



