Nov. is, 1920 Crownwart of Alfalfa Caused by Urophlyctis alfalfae 303 



GROWTH OF THE PARASITE 



The fungus cell thus produced is first uninucleated and bears at its 

 apex a short, cylindrical projection. As it becomes older it increases in 

 size, the single nucleus divides, giving rise to a multinucleated condition, 

 and the short apical projection proliferates more or less successively 

 three or four terminal branches which are directed nearly at right angles 

 to the primary axis. These branches subsequently proliferate usually 

 three to five secondary branches directed in the same plane or forward. 

 As a result of this continued ramification, the larger cells may be seen 

 to bear at their apices an apparatus consisting of a short axial stalk 

 branching to form a score of ultimate terminations. There can be little 

 doubt that these processes function as absorbing organs and may thus 

 be regarded as haustoria. In stained sections they are often too badly 

 obscured by host protoplasm to be readily distinguishable; but in prep- 

 arations of material dissected from fresh, living host plants, they may be 

 studied with ease and certainty. 



In the meantime the turbinate cell has increased considerably in size 

 and in number of nuclei, the latter usually ranging from 10 to 20 or even 

 more. As no septa have appeared, the parasite is represented at this 

 stage by a simple coenocyte. With the cessation of growth by enlarge- 

 ment, this condition is altered by the appearance of a number of delicate 

 septa, the ultimate number usually ranging from 3 to 5 but occasionally 

 even reaching 7, each of which delimits a peripheral uninucleated mass 

 of protoplasm. As the septa do not appear altogether simultaneously, 

 the first to be inserted represent convex membranes united to the periph- 

 eral wall of the turbinate cell along an elliptical line of juncture, the long 

 axis being parallel with the axis of the turbinate cell. The septa in- 

 serted later, when the surface of the turbinate cell has been appropriated 

 in considerable measure, are more likely to be in relation to septa pre- 

 viously laid down as well as to the peripheral wall itself. While the 

 protoplasts first delimited thus tend to approach a double-convex, ellip- 

 tical lenticular shape, the later ones may be more irregular and have 

 several concave facets (Pi. 49, B). 



The further development of each of the peripheral protoplasts thus 

 delimited takes place independently of the other protoplasts similarly 

 derived from the same turbinate cell and follows in the main the course 

 described by Maire and Tison (21) for Urophlyctis hemisphaerica (Speg.) 

 Syd. {U. kriegeriana Magnus) and by Vuillemin (j<5) for U. leproidea. 

 Material embedded in paraffin, sectioned, and stained shows the proto- 

 plasm very slightly contracted away from the septum along the inner sur- 

 face, and indications of such contraction are present also in freshly 

 dissected material mounted in water (PI. 48, B, tb). This slightly con- 

 tracted protoplast now pushes out a protuberance from the outer periph^ 

 eral wall bounding it (PI. 48, C, D, tbx). In those peripheral segments 

 9508 — 20 5 



