juneis, igis Spofigospota Subterrafiea 269 



The stages by which it passes through the limiting membrane and into 

 the protoplasm of the host have not been observed. This is partly due 

 to the fact that most of the cells that are becoming infected or are newly 

 infected are more or less plasmolyzed. Whether this plasmolysis is 

 entirely due to fixation or whether it is in part due to the attack of the 

 Plasmodium is an open question. Numerous cases can be found in 

 which the Plasmodium has not yet gone far into the host protoplast. 

 In such cases it is usually on that side of the cell from which it entered. 

 Other stages can be found in which the plasmodium has just reached 

 the host nucleus. In a later stage it completely or almost completely 

 surrounds the host nucleus. This may properly be considered the last 

 stage of infection. 



The Plasmodium is at no time obviously delimitea from the protoplasm 

 of the host, and there seem to be no membranes between the two. The 

 meshes in the cytoplasm of the plasmodium are smaller than those in 

 the cytoplasm of the host. The parasite takes the orange stain more 

 intensely than the protoplasm of the host. It is therefore easy to dis- 

 tinguish the two, yet they blend into each other in such a way that it is 

 impossible to determine sharply where the one begins and the other leaves 

 off. Thus, the plasmodium in the host cell does not appear to be in a 

 vacuole or to be separated from the host protoplasm by a membrane of 

 any kind. The one seems to be somewhat miscible in the other, which 

 is what might be expected if the surface tensions of the two plasms are 

 equal. Czapek (3) has measured the surface tension of the protoplasm 

 of widely separated groups and has found that in all cases it is approxi- 

 mately the same. This is an interesting point and deserves more detailed 

 study. 



The shape and general macroscopic appearance of the plasmodium as 

 it attacks young potato tissue have already been described. Something 

 should be said of its appearance in stained sections. The cytoplasm of 

 the Plasmodium is finely granular and shows a special affinity for the 

 orange stain. Embedded in it in considerable abundance are the globu- 

 lar bodies that have already been mentioned. They stain very deeply 

 with the gentian violet stain and often appear almost black. Various 

 sizes are to be seen, which have been shown in Plate XXXIX, figures 3, 

 4, 5, 7, 8, and 9. They are also abundant in the photomicrographs 

 shown in Plates XL, XLI, and XLII. The writer has not been able to 

 discover what these bodies are or to observe that they have any specific 

 structure. They are always present and very conspicuous in the infecting 

 Plasmodium and are carried with it into the potato cells. The consid- 

 erable variation in their size and the intensity with which they take the • 

 gentian stain support the view that they may be encysted amoebge that 

 have been engulfed and are carried along. Starch grains, pieces of 

 broken-down cell walls, and other foreign bodies are present in the infect- 

 ing Plasmodium. Nuclei can also be seen, but these are rather difficult 



