44 



CAUSE AND NATURE OF CROWN-GALL 



have repeatedly found them on young galls from the Glendale 

 orchard, on galls from seedlings grown in the green-house and 

 in water cultures. Specimens placed in a hanging drop keep 

 up their movement for one or two days and gradually change 

 to reddish yellow, until finally the organism contracts within 

 the outer membrane into a thick- walled, rather dense cyst 



(Fig. 22). It closely resembles in its 

 behavior the phenomenon observed by 

 De Bary 3<J in isolated cases in Fuligo. 



In certain cells of the diseased tissue 

 peculiar vacuolate, amoeboid, or plas- 

 modium-like structures abound, usu- 

 ally one to several in each cell. They 

 are finely reticulated, and for a time it 

 was thought that they might be the 

 earlier stages of the amoeboid bodies 

 described above. These bodies have 

 been seen to slowly change their form 

 and position (Figs. 23 and 24), pass- 

 ing round the cell from one side to an- 

 other. They may be readily observed 

 in fresh tissue as well as in stained sec- 

 tions, and are rapidly blackened by 

 osmic acid. 



They are surprisingly similar to the 

 " plasmodes " of the so-called Pscudo- 

 commis of Debray and Brive, which 

 more recently have been shown by A. F. Woods" 8 to be noth- 

 ing more than the albuminoid material of dying cells massed 

 together, probably from the effect of slow oxidation. In fixed 

 and stained sections these bodies lose their fine reticulum and 

 usually appear as spherical masses, with a variable number of 

 vacuoles. Repeated tests show the gall tissue to contain much 

 larger quantities of oxidizing enzyme than the normal tissue. 

 If mature galls be cut from the tree in November, placed in 

 moist sand, and kept at a cool, uniform temperature for a week 



39 Morphology and Biology of the Fungi, Mycetozoa, and Bacteria (En- 

 glish translation, Garnsey and Balfour), p. 428. 

 ^Science, N. S., No. 223, p. 508. 



Fig. 22. — Cyst-forming Plas- 

 modium, Nos. 1 and 2, drawn 

 at intervals of two hours the 

 first day after placing in hang- 

 ing drop ; No. 3, the fully- 

 forined cyst of the same indi- 

 vidual, the second day after 

 placing in hanging drop. 

 (Magnified same as scale ; di- 

 visions of scale = 10 ft.) 



