THE PERITHECIUM OF MELIOLA. 11 



from the repeated and rapid division of the cell B, and this view may 

 be recommended on the ground of analogies with the Erysiphece, to be 

 examined hereafter; but, while figs. 19 and 20 by no means decide 

 the point, we shall find that in the perithecium of another species of 

 Meliola (or an allied form) the construction almost certainly proceeds 

 by continued cutting up and " delamination " of the results of division 

 of one cell. 



Be this as it may, the young perithecium now consists of the follow- 

 ing parts : — A central " core " of delicate-walled colourless or yellowish 

 cells, very rich in finely granular protoplasm, and, surrounding this 

 completely, a single layer of cells with thick, hard, dark-coloured walls 

 (especially those on the exterior surface) ; the whole mass is attached 

 to the hypha from which it originated by a very short pedicle or joint 

 (see figs. 19-24). 



At a period slightly later than the above, the cells of the outer 

 layer are becoming multiplied by tangential walls, and those of the 

 inner core by radial and horizontal divisions : these processes go on for 

 some time until the whole perithecium is a complex of many small 

 cells, the outer of which become firmer and darker-coloured, the inner 

 delicate and full of fine-grained protoplasm as described. 



No trace of the internal structure is, however, visible now from the 

 outside. On isolating a perithecium at this stage — a matter of no 

 slight difficulty, but practicable with a slender knife used under a low 

 power of the microscope — it presents the forms shown in fig. 25 

 on being rolled over. Above, the outer surface curves equally away 

 from the centre, and the slightly projecting walls of the cells give it 

 an appearance of being embossed (fig. 25, x). From below (fig. 25, y), 

 the object looks very different ; the surface is much flattened and 

 nearly circular, and from many of the cells are processes developing as 

 hyphee in all directions. These radiating processes creep close along 

 the surface of the leaf, to which the fruit-body is also appressed, and 

 no doubt serve to give a much firmer hold for the fruit ; at first their 

 thin walls are only of a pale brown hue, but rapidly acquire the 

 thickness and deep colour of the fruit and mycelium. Seen from the 

 side, the young perithecium presents the appearance sketched at fig. 

 25, z. It is these radiating anchoring hypha? which form collectively 

 what Bornet terms the "receptacle" and from them, at a later period, 

 the bristling setce found around the mature fruit are developed. 



From the stage just described the development of the fruit-body 



