268 ON THE WHITE BUST OF CABBAGES. 



I was greatly disappointed, on a minute comparison of the 

 flowers and unripe seed-vessels with those in a normal condition, 

 to find that there was no essential derangement of the funda- 

 mental structure, no metamorphosis properly so called, but 

 simply an enlargement of all the parts and a general looseness 

 and hypertrophy in the cellular tissue, arising partly perhaps 

 from the stimulating effect of the mycelium, and partly from the 

 mere mechanical agency of its growth. The dissepiment alone 

 was in proportion far narrower than usual, and extremely deli- 

 cate, as though the placenta had been enlarged at its expense. 

 There was nothing to throw any light on the true import of tlie 

 parts of the carpels, the arrangement of the cellular structure 

 being absolutely the same in both instances, though infested 

 everywhere witli the mycelium. 



It should be observed, that wherever the mycelium did not 

 penetrate, everything presented a perfectly natural appearance 

 without any indication of disease ; nor indeed is there any reason 

 for supposing that a diseased condition of the tissues preceded 

 the growth of the fungus, which in that case would be a mere 

 after-organization. Were tlie fungus in the first instance ex- 

 ternal, tliere might be some shadow of foundation for such an 

 opinion, but the cuticle is perfectly closed till the mass of spores 

 is burst through it, and the sori, as noticed above, make their 

 appearance in the closed cavities of the carpels exactly as Bo- 

 trytis infestans, as observed by Pay en and myself last autumn, 

 in the fruit of the Tomato, where there was no immediate com- 

 munication with the atmosphere. And the case is even stronger 

 in some other fungi, especially in Granularia violcs, Sow., which 

 has not been observed for many years, and had been quite mis- 

 understood till its appearance in Captain Munro's conservatory 

 near Clifton last winter, and (as recorded by Professor Forbes*) 

 in Portland during April of the present year. In that curious 

 production the spores are deeply seated, and the sori do not 

 burst, if they burst at all, till the whole parasite has been long 

 perfectly developed. 



The influence of fungi, however, on perfectly healthy tissues 

 is now an established fact. The case of bunt is a well-known 

 example, the spores of which constantly reproduce the disease ; 

 and if instances are not suificiently satisfactory in the vegetable 

 kingdom, we have only to turn to the facts recorded respecting 

 the origin of the disease of silkworms, called Muscardine, from 

 the spores of a species of Sotrytis, to show that fungi do not 



* In Viola odorata, when attacked by iEcidium violsc, I have seen the 

 stipules assume the form of perfect leaves in consequence of the general 

 luxuriance of the plant. See ' Gardener's Chronicle,' July 1, 1848. 



