354 . H, MARSHALL WARD. 



organs (delicate as they are) become formed. It is not 

 difficult to imagine how, in other Ascomycetes, an advantage 

 was gained when the stroma became fused with the subja- 

 cent epidermis, or leaf tissues ; and it seems clear that the 

 deep shade afforded by the dense walled cells of the disc 

 must be of benefit to the fungus, exposed as it is on the top 

 of the leaf to a tropical sun. If this explanation is the true 

 one, it becomes easier to understand the relations of this 

 fungus, which I will now proceed to examine. 



In the general characters of the mycelium and fruit 

 bodies, as well as in its mode of life, this Ascomycete is 

 clearly a pyrenomycetc apparently allied to the Meliolas,^ 

 several species of which occur in Ceylon ;^ and from the 

 details of structure of the pcrithecimn and spores, it appears 

 probable that it should be placed in the genus Asterina,^ of 

 which it may or may not be a new species. 



Bornet (he. cit.) had already pointed out the analogies 

 between Meliolce and the group of Erysiphei ; and, indeed, 

 it has been assumed that the latter group is represented by 

 the former in the tropics.* The analogies are no less 

 striking, in some respects, with the present fungus; and the 

 discovery of haustoria, which only enter the outer cells of 

 the host, render them still more important. If the structure 

 figured at fig. 17 prove to be a definite Ascogonium, &c., 

 formed on the type of Erysiphe itself, the analogy is ren- 

 dered complete, and the " disc," or stroma, must be looked 

 upon as something superadded. 



As to the injury caused to the individual cells by the 

 haustoria, no direct evidence has been obtained by the use 

 of reagents, &c. No callus or hypertrophy of the invaded 

 tissues can be detected, and it appears highly probable that 

 the parasite only absorbs very soluble, probably largely 

 mineral, contents of the cells. Even when the sickly yellow 

 spots appear the cells do not show obvious injury : each 

 becomes occupied by a single large crystal of calcic oxalate, 

 which, however, appears sooner or later in old leaves not 

 invested by the fungus. No doubt some injury results from 

 the excessive shading, when the black mycelium is abundant 

 on the upper surface ; but there is no evidence to show 

 that the parasitism ever becomes more intense than has been 

 described. 



1 Cf. Bornet's paper in 'Ann. des Sc. Nat.,' torn, xvi, 1851. 



2 Cf. Berkeley and Brown, in 'Jour. Linn. Soc.,' vol. xiv. 



3 ' Bot. Antarctic Voyage,' and 'Joiirn. Linn. Soc.,' vol. xiv. Leveille, 

 'Ann. d. Sc.Nat,,' t. iii, p. 59. 



< See also Berkeley, 'Introd. to Crypt. Bot.,' p. 275, 



