DUBLIN NATUBAL HIBTOBT SOCIETY. 89 



Much of the writings on this subject can be of little or no yalue, be- 

 ing mere theoretic ideas, without sufficient facts to warrant their recep- 

 tion ; still, after laying these aside, we hare a number of positive 

 observations to aid us in determining the truth of those extreme opi- 

 nions, and, as in many other matters, it appears to lie midway between 

 both. To the microscope we owe much of what has already been 

 accomplished in the investigation of these interesting growths and the 

 study of their development, and amongst other remarkable advances in 

 our knowledge we have ascertained by its agency that those lower forms 

 of vegetable life, unlike the higher plants, may have, instead of a single 

 kind of fructification, two, three, four, or even five different modes of 

 reproduction ; and also that, in place of a uniform manner of develop- 

 ing their sti-ucture, they may assume various states under different con- 

 ditions, so unlike each other that nothing but the most ample evidence 

 would enable us to connect them. 



To illustrate my meaning I would merely mention the common and 

 worthless blue mould, Penidllium glaucum, which is considered by our 

 best observers to constitute in another form the well-known yeast plant, 

 or barm, Torula cerevisia^ so important in the process of fermentation 

 and in making bread ; and in still another state it develops into the 

 thick-matted masses of the so-named vinegar plant, which has attracted 

 so much attention in the last few years. 



To prepare for the statements I am about briefly making as to a very 

 common mould producing a diseased state of the hyacinth roots, I may 

 remind you that the silkworm dies of a similar disease (the muscardine, 

 and from a similar cause) a botrytis spreading its mycelium throughout 

 its body, and when it reaches the surface, then alone developing its per- 

 fect fruit, by which time, however, the caterpillar is either dead or its 

 tissues wasted by its parasitic enemy, and its vitality almost gone. The 

 following, too, is the opinion of the Rev. Mr. Berkeley, who holds, per- 

 haps, the foremost rank amongst British authorities on these pests of 

 vegetation, as to the cause of our disastrous potato rot, in his recently 

 published work on Cryptogamic Botany: — "ITn willing as the scientific 

 world has been to allow the agency of fimgi in the potato murrain, as 

 regards that, as well as the grape mildew, there are few dissentient voices 

 now amongst those who understand the subject. The mycelium flou- 

 rishes in the large intercellular spaces of the leaves, but penetrates also 

 into stem and tubers, and at length makes its way either to the external 

 surface or some free cavity, where it finctifies. In a damp warm day 

 the progress of the disease may be watched with ease, and the parasite 

 {Botrytis infestam) may be seen spreading rapidly in a circle, convert- 

 ing all in its way into a mass of decay." He admits, however, that 

 other fungi contribute to the same end. 



I shall now very briefly detail my own observations. I had last 



J rear some remarkably fine hyacinths growing ; they had formed their 

 eaves well and were commencing to bloom, when, after a time, I no- 

 ticed that the expansion of the flowers had been completely checked ; 



