CAUSE AND NATURE OF CROWN-GALL 



43 



cell, in the course of two or three days amoeboid bodies will 

 appear on the cover-glass around the margin of the section. 

 The first appearance of these bodits is as spheres having the 

 granular protoplasmic contents arranged in various bands alter- 

 nating with a perfectly hyaline portion (Fig. 20) and varying 

 from 30 to 50 !>■ in diameter. After a short period of rest the 

 enveloping membrane contracts or is drawn inward in folds, 

 and the plasma becomes diffused. The hyaline portion disap- 

 pears, with the exception of one or more vacuoles. Amoeboid 



Fig. 20.— Amoeboid Plasmodium about 

 to form a thick-walled cyst. Three views 

 of the same individual drawn at intervals 

 of two minutes (Magnified same as scale ; 

 divisions of scale = 10 n). 



Fitt. 21. — Cyst -forming Plasmodium 

 drawn at intervals of one minute, show- 

 ing the rapid changes in the form of the 

 organism (Magnified same as scale ; di- 

 visions of scale = 10 n). 



movement now begins, and the vacuoles vary in size and num- 

 ber in the same individual with more or less rapidity. The 

 organism is now only about one-half the size of its previous 

 spheroidal form. Its transition to the amoeboid form is very 

 rapid. When placed in water it moves with an undulating 

 motion and momentarily varies in form (Fig. 21). As the 

 vacuoles increase in size the surrounding plasma becomes more 

 dense and streaming cytoplasm may be observed within. 



By scraping the surface of young galls that have been kept 

 free from saprophytes it is not difficult to find these bodies. I 



