SPHAERIALES 263 



nucleus. After a considerable resting period the fusion nucleus divides 

 to form eight nuclei; the nuclei pair and migrate into the developing 

 ascogenous hyphae. 



During the resting stage of the fertilized ascogonium large thin- walled 

 cells arise from the basal cell of the archicarp and partially fill the 

 developing perithecium which is formed from hyphal branches of 

 the ascogonial branch. The ascogenous hyphae branch throughout the 

 perithecial cavity between the thin- walled sterile cells and fuse with them 

 or, if sterile cells are not well developed, with the inner cells of the perithe- 

 cial wall, reminding one of the fusions with auxiliary cells by the ooblas- 

 tema filaments in the Florideae. The connections with the original 

 ascogonium disappear, so that by the time the perithecia are matured, the 

 ascogenous cells appear to be arising from the perithecial walls. The asci 

 are first developed basipetally from the top of the perithecium simultane- 

 ously with the beak. No hook formation occurs, the asci being terminal 

 on short branches. The young ascus is binucleate, then the nuclei fuse 

 to a fusion nucleus about half the size of the fusion nucleus of the ascogo- 

 nium. This nucleus divides into eight nuclei which form ascospores about 

 themselves in the usual manner. While the ascospores are still immature 

 the asci disappear leaving the eight more or less associated spores to 

 continue their development in the perithecium (Elliott, 1925). 



In Ceratostoma brevirostre, the unicellular ascogonium is coiled and 

 lacks a distinct trichogyne. It becomes septate and develops ascogenous 

 hyphae (Nichols, 1896). 



In the first group, with perithecia on the upper surface of the sub- 

 strate, certain genera, especially the Trichosphaerieae of the Sphaeriaceae, 

 show a tendency to unite their perithecia on stromata. These forms lead 

 to the second group which normally forms its perithecia on stromata, the 

 Cucurbitariaceae and Coryneliaceae. This coincidence is only external, 

 however. One cannot argue that these stromatic forms (as the stromatic 

 Nectriaceae) have arisen as composites by the crowding of solitary 

 perithecia with a subiculum, but must assume that they belong to 

 essentially different groups, the former to the Dothioraceae-Pseudo- 

 sphaeriaceae line, the latter to the Perisporiales lines; both families have 

 attained the height of their development in the tropics and hence are 

 poorly known. 



Cucurbitariaceae. — The perithecial stromata of this family vary from 

 a thin subiculum to a thick, pulvinate stroma upon which the perithecia 

 are borne. The bases of the perithecia are often partially immersed in 

 the stroma, which is erumpent from the bark. Some species of Cucurbi- 

 taria are wound parasites of roots and branches, as C. Laburni on Labur- 

 num and C. Berberidis on barberry (Welch, 1926). In the chiefly tropical 

 Nitschkia (Fitzpatrick, 1923), the perithecia collapse at maturity and, 

 seen with a hand lens, seem like the mature fertile branches of Mijrian- 



