YEASTS AND MOLDS 315 



As decay of the tomato advances due to the invasion of rotting bacteria, 

 all vegetative cell multiplication of the parasite ceases. Gradually asco- 

 spore formation ceases also and the existing vegetative cells become trans- 

 formed into unusually large, absolutely spherical arthrospores. These 

 arthrospores resemble sphaerocytes very closely. Each cell contains a 

 homogeneous nucleus of very indistinct irregular outline with a more dis- 

 tinct but also homogeneous spherical nucleolus. The plasmic granules 

 are unusually large, spherical in form, highly refractive and stain readily. 

 They are slightly motile and as a rule occur in pairs, resembling diplococci. 

 These plasmic granules occur on the exterior of the homogeneous plasmic 

 supporting substance in this* regard differing from the plasmic granules of 

 chlorophyll bearing plants in which they occur within the plasmic substance. 



The arthrospores occupy a definite position in the medium in which 

 they live (the liquid of the tomato). The nucleus always occupies such 

 a position as to bring the edge of the nucleus into view. Very rarely the 

 spore is sufficiently tilted to present the view indicated in (A), Fig. 

 84. In not a single instance was the spore to be seen in exactly vertical view. 

 No explanation is offered as to why the spore should assume this very 

 definite position. 



Plasmic granules are sparingly present in the vegetal ive cells, from one 

 or two to five whereas in the arthrospores there may be as many as one 

 hundred. As the arthrospores die the plasmic granules apparently 

 increase in number somewhat as some show a remarkable increase in size 

 and they become absolutely motionless. All Brownian vibration ceases 

 also. The plasmic supporting substance shrinks, thus bringing the granules 

 closer together until there is finally a closely crowded mass of plasmic gran- 

 ules as shown in (B), Fig. 84. 



