HIS 



rsn HE. 



( Ausust— SciUcmlier 1SR4. 



centc. Dt'hisceiis non iiiilii obviuiii. In |>l;Mit:i \il>i 

 nccnrrit plerumque fruquenter infesUlt f(>li;i. -Stlnvein- 

 it:, Syn. fuHg. Amer. hnr. {op, cit., p. 241.) 



It li;is been seen tli:it the single or 

 double convexity of tbcse galls is not 

 available as a distinctive character, al- 

 though Schvveinit/. makes use of it. 

 One of the most obvious superficial 

 characters is tlie presence f)r absence of 

 a white, gray or yellow membrane o\ er 

 the carbonized portion of the leaf 

 I'his, the vehdii of Schweinitz, is iiow- 

 ever by no means constantlv absent or 

 present in the same species, if we ex- 

 cept tiiat on Solidago lanceolata, where 

 I have never seen it. On the same 

 plant of .,9. nhjtifolia some spots are 

 black, while others are invested on both 

 surfaces by the vellowisii-white indusi- 

 um : and one of the Osten Sacken tvpes 

 of the gall of C'cc/doi/ivia carboi/ifcra. 

 on a broad leaved Sol/daoo. for an ex- 

 amination of which I am indebted to 

 the courtesv of Dr. fl. A. Hagen. is 

 black above, with a narrow white bor- 

 der, while below It is completelv cov- 

 ered by a white indusium, broken here 

 and there as if by accident. With age 

 this membrane freciuently breaks awav. 

 luit in the specimens to which the pre- 

 cetling statements refer the leaves were 

 intact, and its absence was clearh not 

 due to removal. 



In their microscopic characters, all of 

 these forms show a general agreement. 

 The ]>arenchvnia of the leaf is invaded 

 by a colorless mvccliuni of thick-walled 

 hv])hae. which lives between tin- cells 

 and to a certain extent defornrs them. 

 It excites little if an\ In pertropin . but 

 bv crowding the cells a|)art in its own 



growth causes the slight convexitv of the 

 part of the leaf in which it occurs. 

 Near the surface the uncelial threads 

 become brown, apparentiv as the result 

 of some chemical action due to the fun- 

 gus, which also attects the siuroiniding 

 cells of the leaf, some of which are so 

 completeK carbonized that their walls 

 are coal-black. In A'. so//d<rn-////s and 

 the other exiiuiusiate forms, the epider- 

 mis is especialh influenced b\ this 

 change, which, however sometimes does 

 not extend so far laterallv as in the un- 

 derh iug tissue, — a fact which at once 

 explains the pale border sometimes no- 

 ticed ; the dead but colorless epidermal 

 cells at the margin of the spot, filled 

 with air. appearing white, and contrast- 

 ing stionglv with the carbonized cells 

 on the one hand anil with the living ones 

 on the other. The indusium of the other 

 forms is of a similar nature to this border, 

 consisting merelv of the dead epidermis, 

 tilled with air: but why the epidermis 

 should be blackened in some cases and 

 remain colorless in others it is hard to 

 say . 



Kroui what precedes it will be seen 

 that only two of the three so-called spe- 

 cies of Rhvtisma aie certainlv tlistin- 

 guishable iu the specimens that 1 have 

 examined, \ iz : R. solidaginis. on So- 

 lidairo lanceolata and .V. tcmiifolia. 

 and A^. astcris (including A'. Idfroi/s) 

 on Asfrr and the broader leaved spe- 

 cies of Soh'dago.^ Curtis, whose her- 

 liaiinni. containing manv .^chweinitzian 

 specimens, I have examined, through 



■^ The latter are referred hy Bcrlit-lcy to li. sotiiinjriiiis 

 (Grevillea, v. 4, p. S). 



