i'ri:sii)i:ntjai. AnnKKss— skctiun c. 67 



The most outstanding of the reeent publieations are those 

 of Dr. Erwin ¥. Smith and his colleagues, on the cause of Crown 

 Gall in plants. After a study of some three years, a white 

 bacterium was isolated -from the galls on the Paris daisy, 

 Clirysa)itliciiiitiii fnitcsccns, which, by inoculations with pure 

 cultures produced similar galls on this and a number of other 

 plants beUMiging to several different families (53). This orga- 

 nism is particularly interesting in its action on the plant; it 

 causes a proliferation of the cells, which results in the formation 

 cf ttnnours and in the ])roduction of secondary timiours, at 

 some distance from the ix)int of inoculation. The secondary 

 tmnours are developed on a tumour strand which bores its way 

 through stems or leaves and reproduces' the structure, not of the 

 tissues in which it is found. l)ut of those from which it is 

 derived. 



In a number of pa|)ers ( 55-6 ) Smith has stated his con- 

 viction that these plant galls are similar to malignant animal 

 tumours in several particulars. Some of these are: — permanent 

 and very rapid new growth containing all the tissues of the part 

 attacked : enormous round-celled or spindle-celled hyperplasias, 

 great reduction of the amount of conductive tissues, early 

 necrosis, especially of the more fleshy ttunotn-s, with renewed 

 growth at the margins, frequent recurrence after extirpation, 

 and extension of the disease to other parts by metastases. 



Symbiosis. 



It has been sufficiently proved that bacteria do not occur 

 I'.ormally in the tissues of sound plants. There are. however, 

 certain well-established cases of symbiosis, in which the plant 

 tolerates, or even derives benefit from, the presence of bacteria 

 in its tissues. 



The most familiar example of symbiosis is the relation 

 exi.sting between the Legitiiiiiioscc and the nitrogen-fixing bacteria 

 which inhabit the nodules on their roots. These bacteria are 

 forms which are present somewhat generally in the soil as 

 saprophytes ; they enter the roots of leguminous plants through 

 the root hairs^ exhibiting prochemotactic reactions to certain 

 root excretions, and invade the cells of the root, where the rod- 

 like organisms become metamorphosed into considerably larger, 

 branching structures, the so-called bacterioids. 



To quote a recent text-book (31): "The view once held 

 that the relation between nodule bacteria and host plants is from 

 the start one of true .symbiosis, in which both organisms 

 uniformly derive benefit from the association, has lost gfround in 

 the face of recent researches. .So far from welcoming the advent 

 of Bacillus radicicola to its tissues, the host-plant oflfers a deter- 

 mined resistance. 



" The root hairs ccjnstitute the u>ual portal of entry, and a 

 very definite tissue reaction is produced at the point of invasion. 

 Decided differences in the ' virulence ' of the bacteria are 



