General Features U 



The basal and tip cells each contahi one nucleus while the loop 

 cell contains two. The two nuclei fuse and the loop cell elongates 

 into the ascus. The original nucleus of the ascus which has 

 resulted from the fusion just mentioned divides three or more 

 times, usually giving rise to as many nuclei as there are to be 

 spores in the ascus although some may degenerate or several be 

 included in a single spore. After arranging themselves in the 

 proper position in the ascus, each nucleus surrounds itself with 

 a part of the cytoplasm of the ascus and becomes a spore, sur- 

 rounded with a rather firm wall, the firmness of the wall varying 

 much in different species. 



The development of the spores by the process of free cell 

 formation has been described in detail by R. A. Harper in his 

 studies on Pyronema (Ann. Bot. 14: 363-368). At the pole of 

 each nucleus, after the final division of the fusion nucleus in 

 the ascus, is an aster of fibers which persist and arrange them- 

 selves in the form of a wheel about the beak of the nucleus and 

 finally cut out a nearly spherical mass of cytoplasm which en- 

 closes the nucleus and, wath the development of the wall, becomes 

 the young ascospore. A part of the cytoplasm of the young 

 ascus is used in the formation of the spore and the remainder, 

 which is known as the epiplasm, serves to nourish the young 

 ascospore and to furnish material for the sculpturing of the wall, 

 in those species which have sculptured spores. 



All ascospores are at first smooth and many remain per- 

 manently so. In a number of species of the present group, 

 however, the walls of the mature spores have elaborate markings 

 of a very definite character. These seem to be formed by an 

 accretion of epiplasm about the spore-wall. The process is well 

 illustrated in Sphaerosoma echinulatum of the writer (which in 

 this work is referred to Boiidiera). After the spores are formed 

 in this species, a definite sheath of epiplasm four to five microns 

 thick appears about the spore and is known as the exospore. 

 The sculpturing first appears on the surface of the spore-wail 

 and gradually grows outward until it reaches the outer boundary 

 of the exospore. Even after the sculpturing is completed a 

 definite line persists which marks the outer limits of the original 

 sheath. In other species such as Lamprospora Crec'hqueraullii 

 the sculpturing seems to come about as a gradual growth after 

 the spore is formed. So far as our observations have gone the 

 spores of the operculate cup-fungi are permanently one-celled. 



