THE PERITHECIUM OP MELIOLA. 3 



dental development, so to speak, depending and following upon the 

 formation of the perithecium. 



The mycelium, forming the chief part of the black patches found 

 on the surface of the affected leaves, petioles, &c, spreads in an 

 irregularly stellate manner from a common centre or centres (see 

 fig. 1). It is detached with comparative ease from the epidermis of 

 the leaf, and bristles with fine, simple or branched, pointed appen- 

 dages, of a black colour, which spring from the main hyphae, and 

 from around the subglobular perithecia which are irregularly scattered 

 over the surface. 



The main hyphse constituting this vegetative part of the fungus, 

 are irregularly radiating, sinuous or zigzag filaments, closely appressed 

 to the epidermis of the leaf, &c, and composed of cylindrical joints or 

 cells placed end to end, and branching at angles of about 45 degrees 

 (cf. fig. 2, and fig. 5). Their stiff and even brittle walls are deeply 

 coloured brown or black, and thus obscure the view of their contents : 

 sections and reagents prove these to be finely grained protoplasm, 

 with or without oily drops in the interior. The diameter of the hypha 

 is equal .throughout, the apex being, as a rule, evenly rounded : the 

 cross-septa dividing the hyphee into cells are firmly marked, thick and 

 dark-coloured like the outer walls. 



The main branches of the mycelium all present the same general 

 characters described above. In many cases, however, the blunt apices 

 of the larger hypha?, instead of being evenly rounded, become curiously 

 deformed by an accumulation of abnormal growths, of the nature of 

 caps (see 43, fig. 7) fitting roughly one over the other : these consist 

 of swollen, more or less cuticularised thickenings of the cell-wall, 

 with or without granular debris between the layers. They are evi- 

 dently produced by irregularities in the forward growth of the hypha : 

 in the moist intervals the growing apex, more delicate than the 

 older portions of the hypha, creeps along the surface of the leaf in 

 the normal manner ; during recurrent dry and hot unfavourable 

 periods, however, sudden hardening and stoppage of growth causes 

 the accumulation of the caps. That unfavourable intervals in out= 

 ward circumstances may produce such abnormalities is well seen in 

 the Saprolegnice, and I have in these observed the formation of suc- 

 cessive shell-like caps of dense cellulose, more or less altered, and 

 enclosing granular matter between the layers : the caps are coloured 

 blue by solution of ginc-chloride and iodine, the granular debris yellow t 



