DEVELOPMENT OF THE PERITHECIUM OF MELIOLA. 
589 
step by step on a species of Meliola which I have investigated with no slight success : 
this will be found to throw light on the morphology of these fungi from the best of 
j sources—development—and aid in a more critical estimation of their proposed syste¬ 
matic position. After describing in detail the origin, mode of development and fate 
of the fruit and spores, I propose, therefore, to examine the relations of the Meliolas 
to Erysiphe and other fungi. 
On examining portions of the epipliyllous mycelium bearing the short, pyriform, 
lateral branchlets so often referred to above, one frequently discovers specimens 
presenting the appearances depicted at figs. 9, 10, 11, &c. The simple pyriform body, 
after becoming more swollen, has suffered division into two portions or cells by a 
septum, usually vertical to the plane of the mycelium and leaf, and passing diagonally 
across the cavity with a slight curve, so as to abut on the outer walls at right angles, 
or nearly so. The originally unicellular protuberance becomes in this manner divided 
into two more or less unequal cells, and it will be shown in the sequel that these two 
cells have, from the first, each a different destiny in the formation of the fruit. 
For this reason I have indicated in the drawings, by shading, a difference which does 
not present itself in the natural object at this stage. The more apical cell, which is 
smaller and shaded darker in fig. 9 (Plate 42), may be indicated throughout by the 
letter A : it will be found that this cell produces the central ascogenous tissue of the 
young perithecium, while the other (which will be referred to as cell B) originates the 
outer portions of the case or perithecium wall. 
Following close upon the preliminary division above described, a septum appears 
across the larger of the two cells, cutting the first-formed division wall at right angles, 
or nearly so : this is rapidly followed by another septum (Plate 43, fig. 10), and so the 
larger cell (B) becomes cut up into three. Following upon these, a number of further 
divisions in planes at right angles to the preceding are soon established (figs. 11 to 
17), and at the same time, though much more slowly, one or two more division walls 
are formed in the cell A, thus cutting it up into a short series of about three cells 
(figs. 14, 15). 
If the above description has been followed, it becomes clear that the division of the 
more rapidly growing cell, B, results in the production of a sheet of cells affixed, so 
to speak, to the few-celled mass resulting from the slow division of A : such being 
the case, and the sheet extending as new divisions are formed, the cells resulting from 
A become gradually enveloped more and more in those resulting from B. A com¬ 
parison of the figs. 9 to 17 will facilitate matters here, and for convenience of 
description hereafter, and in consideration of its destiny, we may term the mass of 
cells produced from A the “ascogenous core ”—or simply the core. 
At a stage which may conveniently be considered the next one to fig. 11, the cells 
resulting from the division of B are observed to be extending as a curved layer over 
the “ core ” of cells formed by A. If, at this stage, the young fruit-body is cut off, 
* I must take this opportunity of thanking Professor De Baey for kind suggestions with respect to 
this work. 
MDCCCLXXXIII. 4 G 
