THE PERITHECIUM OF MELIOLA. 9 



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, may be indicated throughout by the letter A : it will be found 

 that this cell produces the central ascogenous tissue of the young 

 peritheciunij 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 (fig. 10), and so the larger cell (B) becomes 

 cut up into three. Following upon these, a number of further divi- 

 sions 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 ex- 

 tending as new divisions are formed, the cells resulting from A become 

 gradually enveloped more and more in those resulting from B. A 

 comparison 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, and allowed to roll 

 over in fluid under the microscope, the form and arrangement are 

 found to be somewhat as sketched in fig. 12, where a represents the 

 view from below, b that from the side, and c an end elevation of the 

 structure. The cell A, in fact, is becoming gradually enfolded by the 

 layer of cells derived from B, a process which results, at a later period 

 (fig. 17), in the almost complete tucking in of the " core " as the centre 

 of a sub-globular mass of cells. 



As this process of " invagination by epibole" (as it would be termed 

 in the case of an embryo) goes on, the " core " has been more slowly 

 cut up into cells — at first by walls perpendicular to its long axis, and 



