OCTOBEE 15, 1915] 



SCIENCE 



537 



since Bubak,^ in his description of this alfalfa 

 leaf-spot, states that a perithecium does not 

 contain more than three or four asci; while, 

 in the material at hand, the number varies 

 from 8 to 14. Furthermore, the ascospore and 

 ascus measurements do not agree entirely with 

 those given by Pollacci,^ or Bubak. Pollacci 

 first reported and named the fungus in Italy. 

 He does not give the number of asci in a 

 perithecium, and his ascospore and ascus meas- 

 urements do not agree with those by Bubak, 

 although the latter regards the species as the 

 same. Puttmans^ describes a variety, naming 

 it Pleosphwrulina Briosiana Pollacci var. Brasi- 

 liensis Puttmans nov. f. He regards it as 

 different from Pleosphcerulina Briosiana Pol- 

 lacci, in that the ascus and ascospore measure- 

 ments are larger. Among the seven species 

 under the genus Pleosphcerulina, described by 

 Saccardo,* including Briosiana, nothing fur- 

 ther is elucidated. 



A description of this alfalfa leaf -spot as it 

 occurs in Kansas is as follows : The spots are 

 scattered irregularly over the entire leaf sur- 

 face, frequently causing spots along the mar- 

 gins. These spots are generally circular or 

 elliptical, from 1 to 5 mm. in diameter. Dur- 

 ing the earliest perceptible stages, the spots 

 appear as very small, dark-reddish-brown spots. 

 These soon increase in size, a dark-brown mar- 

 gin bounding the ashen-gray center of the 

 spot. The centers of these spots may vary from 

 a light tan color to ashen-gray. This tissue 

 does not fall out, but remains intact. The 

 spots are confined almost exclusively to the 

 leaves, but the fungus does attack the petioles. 

 The perithecia are visible to the unaided eye 

 if they are mature, appearing as very small 

 black dots. They occur rather sparingly, ir- 

 regularly and promiscuously scattered within 

 the centers of the spots. They are more or less 

 membranous, partially immersed, erumpent, 

 globular to oblong, slightly pyriform, glabrous, 

 dark brown to black, 100-120jU, in diameter. 

 The asci are ovoid in shape, varying from 8 

 to 12 in number, and measuring 56-75/a long, 

 and 28^2jj, wide. There are no paraphyses, 



4Sylloge Fungorum., Vol. XI., XIV., XVI. 

 and XVII. 



which fact distinguishes this fungus from the 

 genus Catharinia. The asci are supplied with 

 a pedicel at the base, with which they are at- 

 tached to the wall of the perithecium. Each 

 ascus is provided with a peculiar tongue-like 

 projection at the apes, this being a striking 

 characteristic. This does not appear to be de- 

 scribed or mentioned, so far as the writer has 

 been able to find, in Pollacci's description, of 

 this fungus. The ascopores measure 12-14jU, 

 wide, and 30-32,11 long. They are generally 

 arranged so that 5 ascospores are located at 

 the base and larger end of the ascus, and 3 in 

 the upper or narrower part. The spores are 

 multicellular, oblong, fusiform, conspicuously 

 granular, and greenish-hyaline, and having 

 from 3 to 4 septa, and from 1 to 3 longitudinal 

 divisions, making from 5 to 7 cells, rarely 8. 



This leaf-spot may prove to be of consider- 

 able economic importance, since like the 

 Pseudopeziza leaf-spot, it causes destruction 

 of the foliage. 



Leo E. Melchers 



Department op Botany, 

 Kansas State Agriculture College 



differentiation op wandering mesenchymal 



CELLS IN THE LiymG YOLK-SAC 



The yolk-sac of the teleost egg is a partic- 

 ularly favorable object for observing the move- 

 ments and migrations of cells in the develop- 

 ing embryo. Such a yolk-sac has only one 

 really definite continuous membranous cell 

 layer, the ectoderm; a true endodermal layer 

 is absent, though a superficial syncj^tium, the 

 periblast, fuses with the actual yolk surface. 

 The mesodermal layer is represented by numer- 

 ous separate wandering mesenchymal cells. 

 These freely wandering mesenchymal cells may 

 be clearly observed through the perfectly trans- 

 parent ectoderm as they move over the sur- 

 face of the periblast. 



The writer has attempted a detailed study 

 of the movements of the mesenchyme cells and 

 their manner of development and difPerentiation 

 on the yolk-sac. Observations have been made 

 on the normal embryos from the earliest stages 

 at which the mesenchyme wanders out upon. 

 the yolk up to the late embryo in which a com- 



