1914] FROMME—AECIDIUM CUP g 



hyphal mass have their direction of growth toward the center of 

 the mass, a point that usually lies between the first and second 

 layers of host cells. In the very young stages the direction of 

 growth is scarcely evident, since the hyphae wind around the inter- 

 vening host cells; but as the host cells are crowded out and their 

 site filled by branches of the surrounding hyphae or by others that 

 force their way into the mass, it becomes more apparent. Not all 

 of the hyphae are able to reach the center of the mass. Those on 

 its lateral surfaces are crowded out by the earlier formed hyphae 

 within and grow toward the epidermis, encircling the surface of the 

 hyphal mass. There are 5 or 6 layers of these encircling hyphae. 

 The cells that make up the hyphal mass of the young cup are 

 shorter and broader than those of the vegetative mycelium. Their 

 cytoplasm is more dense and stains more deeply. This is particu- 

 larly true of the cells of the interior, while those on the surface of 

 the mass are less sharply differentiated from the purely vegetative 

 cells. As the mass increases in size with the continued destruction 

 of host cells, the fungous cells at the center begin to disintegrate. 

 The first evidence of their disintegration is seen in the appearance 

 of vacuoles in their cytoplasm. This is accompanied by the dis- 

 organization of the nucleus. They become detached from the 

 hyphae on which they are borne and round up and enlarge to two 

 or three times their original size if sufficient space is available. 

 Some of these cells evidently undergo complete disintegration, 

 while others become almost entirely empty except for a few cyto- 

 plasmic shreds and the remnants of the nucleus, and remain for 

 some time in the center of the mass. They often become closely 

 packed together as a result of enlargement, and have the appear- 

 ance of a parenchyma. Because of this condition, this tissue of 

 sterile cells is known as the pseudoparenchyma of the young cup 

 (text fig. 1). 



The first pseudoparenchyma cells formed are the apical cells of 

 the hyphae that converge at the center of the hyphal mass. The 

 disintegration of the cells of these hyphae proceeds from their apices 

 toward their bases, and the area of pseudoparenchyma is increased 

 by the addition of further cells on its margins. The apical surface 

 of the mass is soon reached, and the sterilization of hyphae then 



