1905.] Development of the Ascocarp o/*Humaria granulata. 365 



a decision • as to the etiological distinction of the two generations. It 

 would seem, also, that there must he two reductions, as there are two 

 fusions. The three divisions in the ascus might he expected to show at 

 least one reduction, but Harper (17) is of the opinion that the number of 

 chromosomes remains unaltered during these divisions. Of course, it is 

 possible that the second fusion is of a peculiar nature and does not lead to 

 a doubling of the chromosomes. What is obviously necessary is the dis- 

 covery of a sexual ascomycete with a small number of distinct chromosomes 

 in its nucleus, so that the number can be observed throughout the life- 

 history.* 



De Bary uses the term archicarp as practically synonymous with 

 ascogonium. It seems much more satisfactory to use the term archicarp 

 for the whole fertile branch, apart from the antheridium, and to confine 

 the term ascogonium to that part of the archicarp the contents of which 

 take part in the formation of ascogenous hyphae, i.e., the reproductive 

 cell or cells which contain the female nuclei. It is in this sense that the 

 terms have been used in the body of the paper. Used in this sense the 

 term ascogonium is not necessarily confined to the cell or cells actually 

 giving origin to the ascogenous hyphse. In Ascobolus furfuraceus, for 

 example, the whole curved fertile branch, or scolecite, is the archicarp ; 

 the central part would be the ascogonium, which is divided into a number 

 of cells by a series of perforate septa, as Harper (16) has shown ; only one 

 of the cells of the ascogonium, however, actually gives origin to the ascogenous 

 hyphae, though the contents of all the ascogonial cells pass into this special 

 cell and so into the ascogenous hyphas. In Melanospora parasitica, from the 

 observations of Kihlmanu, the ascogonium is represented by one or two cells 

 of the archicarp, though the cytological details are not known. In Pyronema, 

 Humaria, Sphaerotheca, and Erysiphe the ascogonium is a single cell, and 

 naturally gives origin to one or more ascogenous hyphae. In Collema the 

 archicarp consists of a few small sterile cells at the base, then comes the 

 ascogonium, which is multicellular, and above is the multicellular trichogyne ; 

 all the cells of the ascogonium appear to give origin to ascogenous hyphai. 



* The view that there are two reduction processes is also put forward by Harper in a 

 very important paper ("Sexual Reproduction and the Organization of the Nucleus in 

 certain Mildews,") received while the present paper was passing through the press. 



