ON THE WHITE RUST OF CABBAGES. 



121 



in the published specimens of Kunze, Schmidt, Mougeot, Des- 

 mazieres, Libert, and Rabenhorst, has quite convinced me that 

 there is no peritliecium. In Madame Libert's specimens, Sphaeria 

 maculeeformis, though in an immature condition, as might be 

 expected from its being on leaves which are still green, is inti- 

 mately mixed up with the Septorella. Even in this case, how- 

 ever, the solid contents of the black immature sphaerules suffi- 

 ciently indicate that they have nothing to do with the other 

 fungus, and where both occur isolated from each other there is 

 no difficvdty about the matter. Sometimes the spores of the 

 Septorella ooze out at once from the ruptured cuticle without 

 any thing that might deceive; but occasionally the cellular 

 tissue becomes a little tawny where it is raised up by the sub- 

 jacent spores, which induced Madame Libert to assign a tawny 

 perithecium to the fungus, a very different thing indeed from the 

 black perithecia figured by Greville. When, however, this dis- 

 coloured tissue is removed, there is nothing like the regular 

 cellular structure, which always exists in true perithecia. This fact 

 was pointed out under Cytispora fugax, in the ' English Flora,' 

 in 1836, as completely established by Desmazieres under No. 

 534 of his ' Plantes Cryptogames du Nord,' though it seems to 

 have escaped the notice of later writers, and indeed he has him- 

 self published since a host of species possessing beyond all doubt 

 a rrue perithecium. 



Fig. 1 .—Portion of a patch of Gloeosporium concentn'cum, just after the spores have oozed 

 out, magnifiod. 



Fig. 2.— Ditto where the irrou'ular cirrhi have subsided from moisture, magnified. 



Fi'g. 3.— Section of a leaf, from a firm part destitute ot lacuna?, showing the fungus occu- 

 pying the space which ouglit to be occupied by the subcuticular cells, highly magnified. 



Fig. 4. — Spores and spornjhores, highly magnified. 



Fig. 5.— Spores, still more highly magnified, from a sketch by Mr. Broome. 



VOL. VI. 



