198 CROWN-GALL OF PLANTS. 



on Paris daisy are due to a white schizomycete naraed Bacterium 

 tumefaciens (April, 1907). 



(6) This organism is a short rod multiplying by fission and motile 

 by means of polar flagella. It can be grown in many sorts of culture 

 media, but does not live very long upon agar. It forms small, round, 

 wliite colonies in agar or gelatin poured plates. Under unfavorable 

 conditions of growth it readily develops involution forms. 



(7) This schizomycete differs from many bacterial organisms in 

 not producing open cavities in the plant. It appears to occupy the 

 living cells in small quantities, causing rapid proliferation. 



(8) We have not been able to stain it in the tissues, at least not 

 satisfactorily. 



(9) It is readily plated from young sound galls, i. e., those not 

 fissured or decayed, often in practically pure culture, but it comes up 

 slowly on +15 nutrient agar, and generally not very abundantly. 

 It grows, however, promptly on agar when transferred from cultures. 



(10) It produces galls most readily in soft, rapidly growing tissues. 

 Ordinarily, resting tissues can not be made to produce galls. Turnips 

 seem to be an exception. 



(11) Cross-inoculations to plants of other families have shown 

 the daisy organism to be capable of inducing tumors on many species 

 in widely separate parts of the natural system (Compositae to SaU- 

 caceae), these galls varyifig somewhat in appearance. 



(12) Some species of plants were not infected (onion, fig, olive) 

 and possibly are not infectable, but further experiments should be 

 made. 



(13) For purposes of comparison natural galls have also been 

 studied on the following plants: Peach, apple, rose, quince, honey- 

 suckle, Arhutus unedo, cotton, poplar, chestnut, alfalfa, grape, hop, 

 beet, salsify, turnip, parsnip, lettuce, and willow. 



(14) From all of the preceding, by means of Petri-dish poured plates 

 on agar, scliizomycetes have been isolated closely resembling (as 

 grown on agar) the Bacterium tufnefaciens obtained from the Paris 

 daisy. 



(15) With eight of these organisms tumors have been produced on 

 sound specimens of the species from which obtained. With these eight 

 and two others (not tested on the host) tumors have been produced 

 on daisy and various other plants, thus tending to show a wide range 

 of natural cross-inoculability. 



(16) On pages 133 and 137 the reader will find tables summarizing 

 all the results of the inoculations. 



(17) These organisms have been studied comparatively as to their 

 morphology and cultural characters and found to difl^er only slightly 

 from each other, and from the organism isolated from the daisy, i. e., 

 the agreements are more conspicuous than the differences. 



213 



