40 OUTLINES OF URITISII FUNGOLOGY. 



the ease with which it may be confouiuled with the divided 

 walls of the cells and little fragments which project from 

 them when a section is made for the microscope. At times, 

 however, all difficulty ceases, and in potatoes affected with 

 the Mould which bears so great a part in the production 

 of the Potato murrain 1 have seen instances in which the 

 tissues were almost entirely replaced by the spawn of the 

 Fungus. 



One peculiarity about the growth of Fungi is the tendency 

 which they have to assume a circular disposition, and that not 

 merely in cfases where the spawn is perennial, but where the 

 whole existence of the Fungus is confined to a few days or 

 weeks. A mass of spawn, however, it must be observed, does 

 not arise in general from a single spore, but from a collection 

 of spores, which spread in every direction and form a common 

 felt from whence the fruit rises. I wdll not enter upon the 

 question whether it is possible that several spores, after mak- 

 ing a common felt, may enter into the composition of the 

 same fruit. This is indeed asserted by Ehrenberg, but the 

 point is one of extreme delicacy, and requires much confirma- 

 tion before it can be received as an established fact. Never- 

 theless, as the mass grows from a common centre, it is con- 

 ceivable enough that at a common distance from that centre 

 the spawn should be in a fit condition to produce fruit, and 

 that as it continues to spread, the same process should take 

 place again ; and that, in this way, a concentric arrangement 

 of the fruit should take place, as is the case in some Lichens ; 

 as, for example, in that formerly known under the name of 

 Lichen concentricus.* This disposition is especially evident 

 in some of the parasites which affect fruit, and in none more 

 so than in Oid'ium fruct'if/enum, a Mould which is extremely 

 * Now Lecidea atroalba. 



