94 ON A PECULIAR I'OUM OF MILDEW IN ONIONS. 



the oblong elliptic spores were exposed, still adhering to the tips 

 of the threads, characters belonging manifestly to the genus 

 3Iucor. Tlie sporangia, however, were of exti'eme minuteness, 

 not exceeding in diameter that of the individual cells of tlie onion 

 stem on which they grew ; the appearance, indeed, was that of 

 an Acremonium, but the globular heads of that genus have not 

 been observed to be sporangia, and \yere such indeed the case, 

 there would be no character by which to separate it from 3Iucor 

 except the comparative minuteness.* No columella was observed, 

 but it is possible that in so very minute a body, examined in air 

 without the aid of a liquid medium, which every microscopic 

 observer knows to be of the first importance, it might have been 

 overlooked. One or two very minute species have been observed 

 by authors as Miicor succosus ; by myself, on inspissated sap 

 oozing from the stem of Aucuha Japonica ; Mucor Fimbria, 

 by Nees, and Mucor imperccptihilis, by Sclnank ; but the two 

 former are far larger productions, and the nature of the latter, 

 which grows under water, is extremely uncertain ; and, as Nees 

 von P^senbeck, who has reproduced Sciirank's figures, says ex- 

 pressly, requires fresh observations.! There was some jJeculiar 

 arrangement of the spores within the vesicles, but unfortunately 

 tlie most perfect sketch of the appearance has been mislaid, and, 

 indeed, tlie different stages of growth succeeded each other so 

 rapidly, that it was not sufficiently observed. Tliis was the more 

 to be regretted, as it miglit have thrown some light upon pecu- 

 liar arrangements in otiier moulds, especially in Stilhum pili- 

 forme,\ Corda, where the spores are disposed somewhat in tlie 

 fashion of the cells in the globules of Chara and Nitella. It 

 must be remembered tliat there is good reason to believe with 

 Corda that each sterigraa has the power of producing a succes- 

 sion of spores, which, as they are thrust off by the growth of the 

 new spore, are deposited within tlie vesicle according to mecha- 

 nical laws. The specimen furnished no information as to the 

 development of the fallen spores. 



It appears, then, that the mildew in the instance under con- 

 sideration was due to the presence of a most minute microscopic 

 mould, bearing about the same relation in point of size to the 

 larger species, that Salix herhacea does to well-grown trees 

 of Salix alba. The mould was in every part of the plant con- 

 centrated at numberless points into the form of a Sclerotium, 

 tlius confirming directly the views of Leveille respecting that sup- 

 posed genus. It was observed above that no form of fructifica- 



* I know of no mould so minute except the production described by 

 Niigeli under the generic name of Schinzia penicillata as fructifying in the 

 cells of the roots of an Iris. Linna?a, vol. xvi. p. 278, tab. xi. fig. 2-10. 



f Nees von Esenbeck, Syst. d. Pilz. p. 82. 



X Corda, Ic. Fung., Fasc. III. tab. 2, fig. 41. 



