:»i 



CAUSE AND NATURE <>K CROWN-GALL 



regularly nodular, and sparingly branched, as shown in Fig. 28. 

 The numerous orange-yellow spores usually adhere in clusters 

 and are exceedingly minute, being from 1*2 to 3 />. in diameter, 

 and are frequently flattened at various points by mutual con- 

 tact. They are perfectly smooth, and the comparatively thick 

 episporium, or inclosing membrane, is well defined. The in- 

 closed granular matrix appears homogeneous, or occasionally 

 shows a few bodies of varying size and refractive power im- 

 bedded within it. It is probable that some of these bodies are 

 nuclei; however, I was not able to ascertain their real nature. 



No. 2S — Fragments of the capil 

 litinm, with adhering spore-masses 

 (Magnified same as scale ; scale = 

 10 fi.) 



-& 



i£& d. 



Fig. 29.-0, spores; fi, fragments of the spore 

 membrane after germination ; c. germinating 

 spores; d, swarm-cells, showing cilia; /■, swarm- 

 cells immediately after germination. 



By moistening a needle and inserting the point into a rup- 

 tured sporangium the spores can be conveniently transferred to 

 a hanging drop and their germination studied. The}' begin to 

 germinate almost immediately after being placed in water. The 

 escaping swarm-cells are i}4 :>■ or less in diameter, and at first 

 assume a form nearly spherical and move about with a slight, 

 dancing, vibrator}' motion, but after a time they become pear- 

 shaped and develop an elongated appendage or cilium at the 

 small end, which enables them to move through the water with 

 considerable rapidity. Although in this stage the prevailing 

 form of the swarm-cell is pear-shaped, it varies momentarily in 

 form in the same individual. A small refractive spot, prob- 

 ably a vacuole, was visible in the large end. I was not able to 

 discern nuclei in the swarm-cells with the lens at my command. 



