62 MILDEW OP TPIR 



accompanied by a figure, were published by tlie autlior of this 

 memoir, in the Gardeners' Chronicle, 1851, p. 227, tending to 

 show that in Erysiphe communis, as produced upon the Garden 

 Pea, the sporangia really arose from the decumbent threads of the 

 Oidium, and that in such a way as not to make it probable that 

 this is a case of mere parasitical growth, but that the myceloid 

 threads of the Oidium actually give birth to the Erysiphe, 

 The illustration, if correct, is clearly of great importance ; but 

 inasmuch as it has not been I'eceived with perfect confidence, I am 

 happy to give the annexed figure from the observations of Dr. 

 Plomley, made perfectly independent of my own, which com- 

 pletely confirms the views I liad taken of the matter, and sets it 

 almost beyond doubt (Fig. 1). 



The question was in this state when, in the early part of 1851, 

 a drawing made the previous year by Dr. Plomley, illustrative of 

 the hop mildew, was hung up in the Crystal Palace, in which a 

 transformation of the articulations of the moniliform threads of 

 the Oidium, into what were then supposed to be true sporangia, 

 was clearly represented (Fig. 2). This transformation was pre- 

 cisely like that which so commonly takes place in the genus 

 Antennaria, of which a few words may be said towards the close of 

 the paper. It was not then matter of surprise so far, though it 

 might seem a j^riori scarcely probable that the sporangia should 

 be formed in two different ways, and when the subject was men- 

 tioned in the Gardeners' Chronicle, 1851, p. 467, the interest 

 attached to it was pointed out, though there remained some diffi- 

 culty about the two modes of the origination of sporangia, for the 

 distinction between those organs and others presently to be men- 

 tioned was not at that time ascertained. The correctness of the 

 whole was indeed called in question by Mr. F. J. Graham, in the 

 number of the same year for Aug. 9, p. 502, but so many un- 

 expected circumstances arise in the study of natural histor}', that 

 it is seldom safe to reject altogether any evidence that may be 

 brought forward, because it may at first appear anomalous, how- 

 ever wise it may be to rest in a position of more or less philosophic 

 doubt. In point of fact, such seeming anomalies often indicate 

 latent truths, and when cleared up throw light in the most unlooked 

 for manner on matters which wei'e before involved in obscurity. 

 Recent observations have, indeed, shown that Dr. Plomley 's illus- 

 tration was really of much importance, and the anomalous points 

 have been, for the most part, elucidated by the discovery that the 

 bodies into which the articulations were transformed were not 



