96 ON A PECULIAR FORM OF MILDEW IX ONIONS. 



within the threads and dispersed in the fruit, thus extensively 

 and rapidly propagating the disease. There is no evidence, 

 indeed, to show what was the nature of the mould on the leaves, 

 or whether it was identical with that produced by the mycelium ; 

 but the fact is interesting, as suggesting furtlier observation, and 

 as tending to the establishment of the truth which is so reluc- 

 tantly admitted by many, that fungi are capable of producing 

 extensive disease as well in vegetable as in animal tissues. 



The observation is further important, as showing one way m 

 which fungi may be extensively propagated in the tissue of phje- 

 nogamous plants, when once the mycelium of a mould has been 

 established, for the reproductive bodies produced within the 

 threads, where there was no cavity filled with air proper for the 

 development of the true fruit, miglit be carried by the means of 

 the intercellular passages to any part of the plant ; and it does 

 not follow that these secondary reproductive bodies should always 

 be of the same size as the spores. 



That disease is propagated from one plant to another appears 

 very clear from the two following observations, which I shall 

 give nearly in Mr. Hoffman's own words. A turnip was ob- 

 served, whose leaves were covered with a species of Okhum. A 

 fine half-grown turnip in perfect health happened to be near it, 

 and pushed imprudently one of its leaves in contact with the 

 sickly plant. When first observed, a narrow white velvety bor- 

 der was visible on the edge of the healthy leaf, just where it 

 touched the diseased one. Tlie parasite spread from this border 

 over the whole leaf in a few days, and the poor young turnip 

 fell a sacrifice to bad company, for both decayed. 



Tiie second observation was connected with the grape mildew, 

 which I have described in the Gardener's Chronicle, 1847. Some 

 healthy jjlants of Chrysanthemum Indicum were placed under 

 the vines infested with Oidium Tuckeri, and in a short time 

 every plant was covered with the same fungus. This suggested 

 further experiment. Some self-sown potato plants, of an early 

 variety, entirely free from Botrytis, were potted off, and placed 

 where the Chrysanthemum became diseased. All throve ad- 

 mirably, without exliibiting any appearance of mildew. The 

 grape mould had no eft'ect upoJi them. But when the leaves of 

 a potato infected with Botrytis were shaken over one particular 

 plant, in a few days it was mildewed, the plant became sickly, 

 and eventually died. 



The bearing of all these facts on the possibility of the exten- 

 sive destruction of plants by parasitic moulds is evident, and sug- 

 gests the wisdom of extensive series of well-conducted experi- 

 ments. These, if made without prejudice, or at least with perfect 

 impartiality, would, I am convinced, lead to most important 

 results, which would amply repay the pains bestowed upou them. 



