Frey—Physiology of Venturia Inequalis. 
309 
the perithecium. The stalk cell of the antheridium may also form 
paraphyses. The ascogonium increases in size, the fusion nucleus 
divides and a chain of three to five cells is formed. The end cell 
of the chain is uninucleate, the penultimate cell is generally bi- 
nucleate but may contain more than two nuclei. Branches arise 
from the penultimate cell and perhaps from some of the others; 
these branches are the ascogenous hyphae. The asci are formed 
after the ascogeneous hyphae have become septate. Each ascus 
arises from a terminal cell or as a lateral outgrowth from an inter¬ 
calary cell of an ascogenous hypha. The cells that produce asci 
are at first binucleate. The ascogenous hyphae are multinucleate 
before they become septate which makes it possible to conceive 
that the two nuclei in the ascus are not sister nuclei. Following 
nuclear fusion in the ascus the ascogonium and the sterile cells of 
the ascogenous hyphae degenerate. 
About the time of degeneration of the oogonium the perithecial 
envelope has made considerable growth. The wall formed by the 
perithecial hyphae consists of three layers: a peripheral, or outer 
layer of cells; a protective lignified layer, beneath the peripheral 
layer; and a layer of thin walled nutritive cells in the interior sur¬ 
rounding the asci. Harper has given a detailed account of the 
nuclear behavior in the ascus and the development of the spores; 
these are in agreement with his observations on other forms. 
After the fusion of two nuclei to form the primary ascus nucleus, 
the cytoplasm of the ascus appears spongy but has no large vacu¬ 
oles. Directly after fusion the chromatin of each of the fusing 
nuclei remains independent (retains its individuality), each group 
of chromatic structures consisting of about eight strands. The 
central bodies finally approach and unite, the nucleoli fuse, the 
two groups of chromatin strands intermingle and fusion is com¬ 
plete. At this time the ascus and the perithecium are about half 
grown. A synapsis stage now follows; later the chromatin fibres 
gradually become looser and a spireme appears. Harper always 
found eight chromatin strands at this stage. A period of rest in¬ 
tervenes previous to spindle formation, and the nucleus migrates 
from the base to the middle of the ascus. Each strand of the fibres 
then elongates, becomes bent and forms a chromosome. The chromo¬ 
some contracts and thickens, leaving a fibrillar connection with the 
central body. The chromatin bodies seem to maintain a definite 
connection at all times with the central body. The central body 
now divides, the daughter bodies separate and a spindle is formed 
