no 



PLANT MORPHOLOGY 



the destructive l)lack wart of the potato is caused by Stjnchytrium endo- 

 bioticum. A uniciHate zoospore comes in contact with a young epidermal 

 cell of the host and enters it. Without forming a cell wall, the protoplast 

 of the fungus enlarges and lives symbiotically with the protoplast of the 

 epidermal cell, not killing it but causing it and the adjacent cells of the 



C D 



Fig. 86. Stages in the development of the sporangia of Synchytrium decipiens. A, greatly 

 enlarged fungous protoplast in leaf of host after having destroyed one of its epidermal cells; 

 B, division of large nucleus of fungus to form many small free nuclei; C, cleavage of proto- 

 plast into many small uninucleate cells; D, separation of small cells to form sporangia, 

 each of which has become multinucleate; E, enlarged portion of same; A to D, X125; E, 

 X500. 



host to enlarge. A small gall or blister forms on the surface of the host, 

 this serving as a means by which an infected plant can be recognized. 

 Blisters usually appear both on the leaves and stems. 



Finally, the infected epidermal cell dies. Then the fungus secretes 

 a wall about itself and goes into a resting stage (Fig. 86^). Later 

 its nucleus undergoes repeated divisions and progressive cleavage of the 

 cytoplasm from the surface inward results in the formation of many 

 protoplasts, each of which secretes a wall (Fig. 865, C). These cells 

 may be multinucleate when formed but, if uninucleate, they soon become 

 multinucleate by additional free-nuclear divisions (Fig. 86Z), E). Each 



